Add game lifecycle management and instance import/export tools (#117)

## Summary by Sourcery

Add centralized game process and instance lifecycle management, shared
cache-aware path resolution, and instance import/export/repair
capabilities across backend and UI.

New Features:
- Track a single running game process in the backend, expose stop-game
control, and emit structured game-exited events with instance and
version context.
- Introduce instance path resolution that supports shared caches for
versions, libraries, and assets, and use it across game start, install,
and version management APIs.
- Add import, export, and repair operations for instances, including
zip-based archive support and automatic recovery of on-disk instances.
- Expose new instance lifecycle and repair APIs to the frontend and wire
them through the client and instance store.
- Add per-instance start/stop controls in the instances view and
instance selection in the bottom bar for launching games.

Enhancements:
- Guard instance operations with per-instance locks and track active
operations such as launch, install, delete, and import/export.
- Improve handling of Microsoft login errors and polling status, with
clearer user feedback and safer interval management.
- Simplify config mutation during shared cache migration and centralize
instance directory resolution in the backend.
- Initialize a game lifecycle listener at app startup to keep UI state
in sync with backend game exit events.

Build:
- Configure the Vite dev server to use a fixed localhost host and port
for the UI dev environment.

1 files changed, 5 insertions, 2 deletions

diff --git a/src-tauri/src/core/modpack.rs b/src-tauri/src/core/modpack.rs
index 5ac9493..a580000 100644
--- a/src-tauri/src/core/modpack.rs
+++ b/src-tauri/src/core/modpack.rs
@@ -294,7 +294,7 @@ fn parse_multimc(archive: &mut Archive) -> Result<ParsedModpack, String> {
 
 // ── CurseForge API resolution ─────────────────────────────────────────────
 
-const CURSEFORGE_API_KEY: &str = env!("CURSEFORGE_API_KEY");
+const CURSEFORGE_API_KEY: Option<&str> = option_env!("CURSEFORGE_API_KEY");
 
 async fn resolve_curseforge_files(files: &[ModpackFile]) -> Result<Vec<ModpackFile>, String> {
     let file_ids: Vec<u64> = files
@@ -368,9 +368,12 @@ async fn cf_post(
     endpoint: &str,
     body: &serde_json::Value,
 ) -> Result<serde_json::Value, String> {
+    let api_key = CURSEFORGE_API_KEY
+        .ok_or("CurseForge modpack support requires CURSEFORGE_API_KEY set at build time")?;
+
     let resp = client
         .post(format!("https://api.curseforge.com{endpoint}"))
-        .header("x-api-key", CURSEFORGE_API_KEY)
+        .header("x-api-key", api_key)
         .json(body)
         .send()
         .await