fix: replace intrusive update modal with toast and fix double-restart bug

[k11kirky]

Problem

1. Update-available dialog is a large modal that takes up half the screen and interrupts workflow
2. Users need to press "Restart" twice - first press doesn't actually quit and install the update

Root Cause of Double-Restart Bug

The installUpdate() method called shutdown() which tore down the DI container before quitAndInstall() triggered the before-quit event. When the before-quit handler tried to access the container, it threw an error, preventing a clean quit. On a second press, shutdown() sees _isShuttingDown=true and calls forceExit(), killing the process without the updater installing.

Changes

1. Fix double-restart bug

• Added cleanupForUpdate() method to AppLifecycleService that does essential cleanup (killing processes, shutting down watchers) without tearing down the DI container
• Updated UpdatesService.installUpdate() to:
  1. Set isQuittingForUpdate flag FIRST
  2. Call cleanupForUpdate() instead of shutdown()
  3. Then call quitAndInstall()

This ensures the container stays intact for the before-quit handler while still properly cleaning up processes and watchers.

2. Replace update modal with persistent toast

• Rewrote UpdatePrompt.tsx to show a persistent toast (duration: Infinity) in the bottom right when an update is ready
• Includes inline "Restart now" and "Later" action buttons directly in the toast
• Uses stable toast ID for proper dismissal
• Kept "Check for Updates" dialog unchanged (only shown on manual menu action)

3. Update tests

• Added cleanupForUpdate mock to lifecycle service tests
• Verified correct call order: setQuittingForUpdate() → cleanupForUpdate() → quitAndInstall()
• Ensured shutdown() is NOT called during update installation

Testing

Automated

• ✅ All 245 tests pass
• ✅ Typecheck passes

Manual Testing (Production Build Required)

Updates are only enabled in packaged/production builds, so manual testing requires:

1. Test the toast notification:

   • Build and package the app
   • Trigger an update check when a new version is available
   • Verify the toast appears in the bottom right (not a large modal)
   • Verify it persists until action is taken

2. Test single-restart:

   • When update is ready, click "Restart now"
   • Verify the app quits and installs the update on the FIRST click (not requiring a second press)
   • Verify the app restarts with the new version

3. Test "Later" action:

   • Click "Later" button
   • Verify the toast dismisses
   • Verify you can continue working

Files Modified

• apps/twig/src/main/services/app-lifecycle/service.ts - added cleanupForUpdate() method
• apps/twig/src/main/services/updates/service.ts - fixed install flow
• apps/twig/src/main/services/updates/service.test.ts - updated tests
• apps/twig/src/renderer/components/UpdatePrompt.tsx - replaced modal with toast

[k11kirky]

closes #814