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, 7 insertions, 0 deletions

diff --git a/.env.example b/.env.example
new file mode 100644
index 0000000..9e7e55a
--- /dev/null
+++ b/.env.example
@@ -0,0 +1,7 @@
+# Copy this file to .env and fill in values to enable optional features at build time.
+# .env is gitignored and will never be committed.
+
+# CurseForge API key — required only to build with CurseForge modpack support.
+# Obtain one at https://console.curseforge.com/
+# If absent, CurseForge modpack import is disabled at runtime (all other features work normally).
+# CURSEFORGE_API_KEY=your_key_here