feat(frontend): add instance editor modal with tabbed interface

- Create InstanceEditorModal.svelte with 4 tabs:
  * Info: Instance name, notes, metadata (created date, last played)
  * Version: Mod loader switcher and version display
  * Files: File browser for mods/resourcepacks/shaderpacks/saves/screenshots
  * Settings: Memory override and JVM arguments customization
- Wire InstanceEditorModal to InstancesView with Edit button
- Add FileInfo type definition to types/index.ts
- Fix accessibility issues: proper button roles, keyboard events
- All TypeScript and Svelte compilation errors resolved
- Enable comprehensive per-instance configuration management

3 files changed, 464 insertions, 50 deletions

diff --git a/ui/src/components/InstanceEditorModal.svelte b/ui/src/components/InstanceEditorModal.svelte
new file mode 100644
index 0000000..0856d93
--- /dev/null
+++ b/ui/src/components/InstanceEditorModal.svelte
@@ -0,0 +1,439 @@
+<script lang="ts">
+  import { invoke } from "@tauri-apps/api/core";
+  import { X, Save, Loader2, Trash2, FolderOpen } from "lucide-svelte";
+  import { instancesState } from "../stores/instances.svelte";
+  import { gameState } from "../stores/game.svelte";
+  import { settingsState } from "../stores/settings.svelte";
+  import type { Instance, FileInfo, FabricLoaderEntry, ForgeVersion } from "../types";
+  import ModLoaderSelector from "./ModLoaderSelector.svelte";
+
+  interface Props {
+    isOpen: boolean;
+    instance: Instance | null;
+    onClose: () => void;
+  }
+
+  let { isOpen, instance, onClose }: Props = $props();
+
+  // Tabs: "info" | "version" | "files" | "settings"
+  let activeTab = $state<"info" | "version" | "files" | "settings">("info");
+  let saving = $state(false);
+  let errorMessage = $state("");
+
+  // Info tab state
+  let editName = $state("");
+  let editNotes = $state("");
+
+  // Version tab state
+  let fabricLoaders = $state<FabricLoaderEntry[]>([]);
+  let forgeVersions = $state<ForgeVersion[]>([]);
+  let loadingVersions = $state(false);
+
+  // Files tab state
+  let selectedFileFolder = $state<"mods" | "resourcepacks" | "shaderpacks" | "saves" | "screenshots">("mods");
+  let fileList = $state<FileInfo[]>([]);
+  let loadingFiles = $state(false);
+  let deletingPath = $state<string | null>(null);
+
+  // Settings tab state
+  let editMemoryMin = $state(0);
+  let editMemoryMax = $state(0);
+  let editJavaArgs = $state("");
+
+  // Initialize form when instance changes
+  $effect(() => {
+    if (isOpen && instance) {
+      editName = instance.name;
+      editNotes = instance.notes || "";
+      editMemoryMin = instance.memory_override?.min || settingsState.settings.min_memory || 512;
+      editMemoryMax = instance.memory_override?.max || settingsState.settings.max_memory || 2048;
+      editJavaArgs = instance.jvm_args_override || "";
+      errorMessage = "";
+    }
+  });
+
+  // Load files when switching to files tab
+  $effect(() => {
+    if (isOpen && instance && activeTab === "files") {
+      loadFileList();
+    }
+  });
+
+  // Load file list for selected folder
+  async function loadFileList() {
+    if (!instance) return;
+    
+    loadingFiles = true;
+    try {
+      const files = await invoke<FileInfo[]>("list_instance_directory", {
+        instanceId: instance.id,
+        folder: selectedFileFolder,
+      });
+      fileList = files;
+    } catch (err) {
+      errorMessage = `Failed to load files: ${err}`;
+      fileList = [];
+    } finally {
+      loadingFiles = false;
+    }
+  }
+
+  // Change selected folder and reload
+  async function changeFolder(folder: "mods" | "resourcepacks" | "shaderpacks" | "saves" | "screenshots") {
+    selectedFileFolder = folder;
+    await loadFileList();
+  }
+
+  // Delete a file or directory
+  async function deleteFile(filePath: string) {
+    if (!confirm(`Are you sure you want to delete "${filePath.split("/").pop()}"?`)) {
+      return;
+    }
+
+    deletingPath = filePath;
+    try {
+      await invoke("delete_instance_file", { path: filePath });
+      // Reload file list
+      await loadFileList();
+    } catch (err) {
+      errorMessage = `Failed to delete file: ${err}`;
+    } finally {
+      deletingPath = null;
+    }
+  }
+
+  // Open file in system explorer
+  async function openInExplorer(filePath: string) {
+    try {
+      await invoke("open_file_explorer", { path: filePath });
+    } catch (err) {
+      errorMessage = `Failed to open file explorer: ${err}`;
+    }
+  }
+
+  // Save instance changes
+  async function saveChanges() {
+    if (!instance) return;
+    if (!editName.trim()) {
+      errorMessage = "Instance name cannot be empty";
+      return;
+    }
+
+    saving = true;
+    errorMessage = "";
+
+    try {
+      const updatedInstance: Instance = {
+        ...instance,
+        name: editName.trim(),
+        notes: editNotes.trim() || undefined,
+        memory_override: {
+          min: editMemoryMin,
+          max: editMemoryMax,
+        },
+        jvm_args_override: editJavaArgs.trim() || undefined,
+      };
+
+      await instancesState.updateInstance(updatedInstance);
+      onClose();
+    } catch (err) {
+      errorMessage = `Failed to save instance: ${err}`;
+    } finally {
+      saving = false;
+    }
+  }
+
+  function formatFileSize(bytes: number): string {
+    if (bytes === 0) return "0 B";
+    const k = 1024;
+    const sizes = ["B", "KB", "MB", "GB"];
+    const i = Math.floor(Math.log(bytes) / Math.log(k));
+    return Math.round((bytes / Math.pow(k, i)) * 100) / 100 + " " + sizes[i];
+  }
+
+  function formatDate(timestamp: number): string {
+    return new Date(timestamp * 1000).toLocaleDateString();
+  }
+</script>
+
+{#if isOpen && instance}
+  <div
+    class="fixed inset-0 z-[100] bg-black/80 backdrop-blur-sm flex items-center justify-center p-4"
+    role="dialog"
+    aria-modal="true"
+  >
+    <div
+      class="bg-zinc-900 border border-zinc-700 rounded-xl shadow-2xl w-full max-w-4xl max-h-[90vh] overflow-hidden flex flex-col"
+    >
+      <!-- Header -->
+      <div class="flex items-center justify-between p-6 border-b border-zinc-700">
+        <div>
+          <h2 class="text-xl font-bold text-white">Edit Instance</h2>
+          <p class="text-sm text-zinc-400 mt-1">{instance.name}</p>
+        </div>
+        <button
+          onclick={onClose}
+          disabled={saving}
+          class="p-2 rounded-lg hover:bg-zinc-800 text-zinc-400 hover:text-white transition-colors disabled:opacity-50"
+        >
+          <X size={20} />
+        </button>
+      </div>
+
+      <!-- Tab Navigation -->
+      <div class="flex gap-1 px-6 pt-4 border-b border-zinc-700">
+        {#each [
+          { id: "info", label: "Info" },
+          { id: "version", label: "Version" },
+          { id: "files", label: "Files" },
+          { id: "settings", label: "Settings" },
+        ] as tab}
+          <button
+            onclick={() => (activeTab = tab.id as any)}
+            class="px-4 py-2 text-sm font-medium transition-colors rounded-t-lg {activeTab === tab.id
+              ? 'bg-indigo-600 text-white'
+              : 'bg-zinc-800 text-zinc-400 hover:text-white'}"
+          >
+            {tab.label}
+          </button>
+        {/each}
+      </div>
+
+      <!-- Content Area -->
+      <div class="flex-1 overflow-y-auto p-6">
+        {#if activeTab === "info"}
+          <!-- Info Tab -->
+          <div class="space-y-4">
+            <div>
+              <label for="instance-name" class="block text-sm font-medium text-white/90 mb-2">
+                Instance Name
+              </label>
+              <input
+                id="instance-name"
+                type="text"
+                bind:value={editName}
+                class="w-full px-4 py-2 bg-zinc-800 border border-zinc-700 rounded-lg text-white placeholder-zinc-500 focus:outline-none focus:ring-2 focus:ring-indigo-500"
+                disabled={saving}
+              />
+            </div>
+
+            <div>
+              <label for="instance-notes" class="block text-sm font-medium text-white/90 mb-2">
+                Notes
+              </label>
+              <textarea
+                id="instance-notes"
+                bind:value={editNotes}
+                rows="4"
+                placeholder="Add notes about this instance..."
+                class="w-full px-4 py-2 bg-zinc-800 border border-zinc-700 rounded-lg text-white placeholder-zinc-500 focus:outline-none focus:ring-2 focus:ring-indigo-500 resize-none"
+                disabled={saving}
+              ></textarea>
+            </div>
+
+            <div class="grid grid-cols-2 gap-4 text-sm">
+              <div class="p-3 bg-zinc-800 rounded-lg">
+                <p class="text-zinc-400">Created</p>
+                <p class="text-white font-medium">{formatDate(instance.created_at)}</p>
+              </div>
+              <div class="p-3 bg-zinc-800 rounded-lg">
+                <p class="text-zinc-400">Last Played</p>
+                <p class="text-white font-medium">
+                  {instance.last_played ? formatDate(instance.last_played) : "Never"}
+                </p>
+              </div>
+              <div class="p-3 bg-zinc-800 rounded-lg">
+                <p class="text-zinc-400">Game Directory</p>
+                <p class="text-white font-medium text-xs truncate" title={instance.game_dir}>
+                  {instance.game_dir.split("/").pop()}
+                </p>
+              </div>
+              <div class="p-3 bg-zinc-800 rounded-lg">
+                <p class="text-zinc-400">Current Version</p>
+                <p class="text-white font-medium">{instance.version_id || "None"}</p>
+              </div>
+            </div>
+          </div>
+        {:else if activeTab === "version"}
+          <!-- Version Tab -->
+          <div class="space-y-4">
+            {#if instance.version_id}
+              <div class="p-4 bg-indigo-500/10 border border-indigo-500/30 rounded-lg">
+                <p class="text-sm text-indigo-400">
+                  Currently playing: <span class="font-medium">{instance.version_id}</span>
+                  {#if instance.mod_loader}
+                    with <span class="capitalize">{instance.mod_loader}</span>
+                    {instance.mod_loader_version && `${instance.mod_loader_version}`}
+                  {/if}
+                </p>
+              </div>
+            {/if}
+
+            <div>
+              <h3 class="text-sm font-medium text-white/90 mb-4">Change Version or Mod Loader</h3>
+              <ModLoaderSelector
+                selectedGameVersion={instance.version_id || ""}
+                onInstall={(versionId) => {
+                  // Version installed, update instance version_id
+                  instance.version_id = versionId;
+                  saveChanges();
+                }}
+              />
+            </div>
+          </div>
+        {:else if activeTab === "files"}
+          <!-- Files Tab -->
+          <div class="space-y-4">
+            <div class="flex gap-2 flex-wrap">
+              {#each ["mods", "resourcepacks", "shaderpacks", "saves", "screenshots"] as folder}
+                <button
+                  onclick={() => changeFolder(folder as any)}
+                  class="px-3 py-1.5 rounded-lg text-sm font-medium transition-colors {selectedFileFolder ===
+                  folder
+                    ? "bg-indigo-600 text-white"
+                    : "bg-zinc-800 text-zinc-400 hover:text-white"}"
+                >
+                  {folder}
+                </button>
+              {/each}
+            </div>
+
+            {#if loadingFiles}
+              <div class="flex items-center gap-2 text-zinc-400 py-8 justify-center">
+                <Loader2 size={16} class="animate-spin" />
+                Loading files...
+              </div>
+            {:else if fileList.length === 0}
+              <div class="text-center py-8 text-zinc-500">
+                No files in this folder
+              </div>
+            {:else}
+              <div class="space-y-2">
+                {#each fileList as file}
+                  <div
+                    class="flex items-center justify-between p-3 bg-zinc-800 rounded-lg hover:bg-zinc-700 transition-colors"
+                  >
+                    <div class="flex-1 min-w-0">
+                      <p class="font-medium text-white truncate">{file.name}</p>
+                      <p class="text-xs text-zinc-400">
+                        {file.is_directory ? "Folder" : formatFileSize(file.size)}
+                        • {formatDate(file.modified)}
+                      </p>
+                    </div>
+                    <div class="flex gap-2 ml-4">
+                      <button
+                        onclick={() => openInExplorer(file.path)}
+                        title="Open in explorer"
+                        class="p-2 rounded-lg hover:bg-zinc-600 text-zinc-400 hover:text-white transition-colors"
+                      >
+                        <FolderOpen size={16} />
+                      </button>
+                      <button
+                        onclick={() => deleteFile(file.path)}
+                        disabled={deletingPath === file.path}
+                        title="Delete"
+                        class="p-2 rounded-lg hover:bg-red-600/20 text-red-400 hover:text-red-300 transition-colors disabled:opacity-50"
+                      >
+                        {#if deletingPath === file.path}
+                          <Loader2 size={16} class="animate-spin" />
+                        {:else}
+                          <Trash2 size={16} />
+                        {/if}
+                      </button>
+                    </div>
+                  </div>
+                {/each}
+              </div>
+            {/if}
+          </div>
+        {:else if activeTab === "settings"}
+          <!-- Settings Tab -->
+          <div class="space-y-4">
+            <div>
+              <label for="min-memory" class="block text-sm font-medium text-white/90 mb-2">
+                Minimum Memory (MB)
+              </label>
+              <input
+                id="min-memory"
+                type="number"
+                bind:value={editMemoryMin}
+                min="256"
+                max={editMemoryMax}
+                class="w-full px-4 py-2 bg-zinc-800 border border-zinc-700 rounded-lg text-white focus:outline-none focus:ring-2 focus:ring-indigo-500"
+                disabled={saving}
+              />
+              <p class="text-xs text-zinc-400 mt-1">
+                Default: {settingsState.settings.min_memory}MB
+              </p>
+            </div>
+
+            <div>
+              <label for="max-memory" class="block text-sm font-medium text-white/90 mb-2">
+                Maximum Memory (MB)
+              </label>
+              <input
+                id="max-memory"
+                type="number"
+                bind:value={editMemoryMax}
+                min={editMemoryMin}
+                max="16384"
+                class="w-full px-4 py-2 bg-zinc-800 border border-zinc-700 rounded-lg text-white focus:outline-none focus:ring-2 focus:ring-indigo-500"
+                disabled={saving}
+              />
+              <p class="text-xs text-zinc-400 mt-1">
+                Default: {settingsState.settings.max_memory}MB
+              </p>
+            </div>
+
+            <div>
+              <label for="java-args" class="block text-sm font-medium text-white/90 mb-2">
+                JVM Arguments (Advanced)
+              </label>
+              <textarea
+                id="java-args"
+                bind:value={editJavaArgs}
+                rows="4"
+                placeholder="-XX:+UnlockExperimentalVMOptions -XX:G1NewCollectionPercentage=20..."
+                class="w-full px-4 py-2 bg-zinc-800 border border-zinc-700 rounded-lg text-white placeholder-zinc-500 focus:outline-none focus:ring-2 focus:ring-indigo-500 font-mono text-sm resize-none"
+                disabled={saving}
+              ></textarea>
+              <p class="text-xs text-zinc-400 mt-1">
+                Leave empty to use global Java arguments
+              </p>
+            </div>
+          </div>
+        {/if}
+
+        {#if errorMessage}
+          <div class="mt-4 p-3 bg-red-500/10 border border-red-500/30 rounded-lg text-red-400 text-sm">
+            {errorMessage}
+          </div>
+        {/if}
+      </div>
+
+      <!-- Footer -->
+      <div class="flex items-center justify-end gap-3 p-6 border-t border-zinc-700">
+        <button
+          onclick={onClose}
+          disabled={saving}
+          class="px-4 py-2 rounded-lg bg-zinc-800 hover:bg-zinc-700 text-white transition-colors disabled:opacity-50"
+        >
+          Cancel
+        </button>
+        <button
+          onclick={saveChanges}
+          disabled={saving || !editName.trim()}
+          class="px-4 py-2 rounded-lg bg-indigo-600 hover:bg-indigo-500 text-white transition-colors disabled:opacity-50 flex items-center gap-2"
+        >
+          {#if saving}
+            <Loader2 size={16} class="animate-spin" />
+            Saving...
+          {:else}
+            <Save size={16} />
+            Save Changes
+          {/if}
+        </button>
+      </div>
+    </div>
+  </div>
+{/if}
diff --git a/ui/src/components/InstancesView.svelte b/ui/src/components/InstancesView.svelte
index e42f813..5334f9e 100644
--- a/ui/src/components/InstancesView.svelte
+++ b/ui/src/components/InstancesView.svelte
@@ -4,12 +4,14 @@
   import { Plus, Trash2, Edit2, Copy, Check, X } from "lucide-svelte";
   import type { Instance } from "../types";
   import InstanceCreationModal from "./InstanceCreationModal.svelte";
+  import InstanceEditorModal from "./InstanceEditorModal.svelte";
 
   let showCreateModal = $state(false);
   let showEditModal = $state(false);
   let showDeleteConfirm = $state(false);
   let showDuplicateModal = $state(false);
   let selectedInstance: Instance | null = $state(null);
+  let editingInstance: Instance | null = $state(null);
   let newInstanceName = $state("");
   let duplicateName = $state("");
 
@@ -22,9 +24,7 @@
   }
 
   function handleEdit(instance: Instance) {
-    selectedInstance = instance;
-    newInstanceName = instance.name;
-    showEditModal = true;
+    editingInstance = instance;
   }
 
   function handleDelete(instance: Instance) {
@@ -38,17 +38,6 @@
     showDuplicateModal = true;
   }
 
-  async function confirmEdit() {
-    if (!selectedInstance || !newInstanceName.trim()) return;
-    await instancesState.updateInstance({
-      ...selectedInstance,
-      name: newInstanceName.trim(),
-    });
-    showEditModal = false;
-    selectedInstance = null;
-    newInstanceName = "";
-  }
-
   async function confirmDelete() {
     if (!selectedInstance) return;
     await instancesState.deleteInstance(selectedInstance.id);
@@ -104,10 +93,13 @@
     <div class="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-4">
       {#each instancesState.instances as instance (instance.id)}
         <div
+          role="button"
+          tabindex="0"
           class="relative p-4 bg-gray-100 dark:bg-gray-800 rounded-lg border-2 transition-all cursor-pointer hover:border-blue-500 {instancesState.activeInstanceId === instance.id
             ? 'border-blue-500'
             : 'border-transparent'}"
           onclick={() => instancesState.setActiveInstance(instance.id)}
+          onkeydown={(e) => e.key === "Enter" && instancesState.setActiveInstance(instance.id)}
         >
           {#if instancesState.activeInstanceId === instance.id}
             <div class="absolute top-2 right-2">
@@ -121,6 +113,7 @@
             </h3>
             <div class="flex gap-1">
               <button
+                type="button"
                 onclick={(e) => {
                   e.stopPropagation();
                   handleEdit(instance);
@@ -131,6 +124,7 @@
                 <Edit2 size={16} class="text-gray-600 dark:text-gray-400" />
               </button>
               <button
+                type="button"
                 onclick={(e) => {
                   e.stopPropagation();
                   handleDuplicate(instance);
@@ -141,6 +135,7 @@
                 <Copy size={16} class="text-gray-600 dark:text-gray-400" />
               </button>
               <button
+                type="button"
                 onclick={(e) => {
                   e.stopPropagation();
                   handleDelete(instance);
@@ -190,41 +185,14 @@
 <!-- Create Modal -->
 <InstanceCreationModal isOpen={showCreateModal} onClose={() => (showCreateModal = false)} />
 
-<!-- Edit Modal -->
-{#if showEditModal && selectedInstance}
-  <div class="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50">
-    <div class="bg-white dark:bg-gray-800 rounded-lg p-6 w-96">
-      <h2 class="text-xl font-bold mb-4 text-gray-900 dark:text-white">Edit Instance</h2>
-      <input
-        type="text"
-        bind:value={newInstanceName}
-        placeholder="Instance name"
-        class="w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white mb-4"
-        onkeydown={(e) => e.key === "Enter" && confirmEdit()}
-        autofocus
-      />
-      <div class="flex gap-2 justify-end">
-        <button
-          onclick={() => {
-            showEditModal = false;
-            selectedInstance = null;
-            newInstanceName = "";
-          }}
-          class="px-4 py-2 bg-gray-200 dark:bg-gray-700 text-gray-900 dark:text-white rounded-lg hover:bg-gray-300 dark:hover:bg-gray-600 transition-colors"
-        >
-          Cancel
-        </button>
-        <button
-          onclick={confirmEdit}
-          disabled={!newInstanceName.trim()}
-          class="px-4 py-2 bg-blue-600 text-white rounded-lg hover:bg-blue-700 disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
-        >
-          Save
-        </button>
-      </div>
-    </div>
-  </div>
-{/if}
+<!-- Instance Editor Modal -->
+<InstanceEditorModal
+  isOpen={editingInstance !== null}
+  instance={editingInstance}
+  onClose={() => {
+    editingInstance = null;
+  }}
+/>
 
 <!-- Delete Confirmation -->
 {#if showDeleteConfirm && selectedInstance}
@@ -266,7 +234,6 @@
         placeholder="New instance name"
         class="w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white mb-4"
         onkeydown={(e) => e.key === "Enter" && confirmDuplicate()}
-        autofocus
       />
       <div class="flex gap-2 justify-end">
         <button
diff --git a/ui/src/types/index.ts b/ui/src/types/index.ts
index 6632d58..b4412b8 100644
--- a/ui/src/types/index.ts
+++ b/ui/src/types/index.ts
@@ -222,3 +222,11 @@ export interface MemoryOverride {
   min: number; // MB
   max: number; // MB
 }
+
+export interface FileInfo {
+  name: string;
+  path: string;
+  is_directory: boolean;
+  size: number;
+  modified: number;
+}