feat: add close confirmation modal with minimize to tray option

Implemented a confirmation modal when users try to close the application:
- Modal always shows with three options: Cancel, Minimize to Tray, Close Application
- Detects if Claude is actively running and shows appropriate warning message
- Removed minimize_to_tray config setting (no longer needed)
- Added core:window:allow-hide permission for window hiding
- Created CloseAppConfirmModal component with keyboard shortcuts (Escape to cancel)
- Added close_application command to properly exit the app
- Backend emits window-close-requested event for frontend to handle

This provides better UX by giving users clear choices every time they close,
preventing accidental closures during active work sessions.

src-tauri/capabilities/default.json

@@ -30,6 +30,7 @@
     },
     "core:window:allow-set-size",
     "core:window:allow-set-always-on-top",
-    "core:window:allow-inner-size"
+    "core:window:allow-inner-size",
+    "core:window:allow-hide"
   ]
 }