feat(notifications): add notification history panel and overlay UX fixes

- New toggleNotificationHistory (Ctrl+N) session-scoped history panel; slides in from same edge as notification stack
- Overlay error/recovery toast follows notifications.overlayPosition; stack and history side seeded at startup
- Cold managed background startup initializes tray and visible overlay shell before tokenization warmups finish
- Add Update button to overlay update-available notifications
- Fix Ctrl+S sentence-card flow: only Anki progress notification, no duplicate status toast
- Fix overlay notification close/actions clickability above subtitle bars on Linux
- Increase pause-until-ready default timeout from 15s to 30s

src/renderer/handlers/keyboard.test.ts

@@ -94,6 +94,7 @@ function createEmptyShortcuts(): ConfiguredShortcuts {
     openControllerSelect: null,
     openControllerDebug: null,
     toggleSubtitleSidebar: null,
+    toggleNotificationHistory: null,
   };
 }
 
@@ -133,6 +134,7 @@ function installKeyboardTestGlobals() {
     openControllerSelect: 'Alt+C',
     openControllerDebug: 'Alt+Shift+C',
     toggleSubtitleSidebar: '',
+    toggleNotificationHistory: '',
     toggleVisibleOverlayGlobal: '',
   };
   let markActiveVideoWatchedResult = true;
@@ -1178,6 +1180,7 @@ test('refreshConfiguredShortcuts updates hot-reloaded stats and watched keys', a
       openControllerSelect: 'Alt+C',
       openControllerDebug: 'Alt+Shift+C',
       toggleSubtitleSidebar: '',
+      toggleNotificationHistory: '',
       toggleVisibleOverlayGlobal: '',
     });
     testGlobals.setStatsToggleKey('');