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/core/services/session-actions.ts

@@ -14,6 +14,7 @@ export interface SessionActionExecutorDeps {
   mineSentenceCount: (count: number) => void;
   toggleSecondarySub: () => void;
   toggleSubtitleSidebar: () => void;
+  toggleNotificationHistory: () => void;
   markLastCardAsAudioCard: () => Promise<void>;
   markActiveVideoWatched: () => Promise<boolean>;
   openRuntimeOptionsPalette: () => void;
@@ -79,6 +80,9 @@ export async function dispatchSessionAction(
     case 'toggleSubtitleSidebar':
       deps.toggleSubtitleSidebar();
       return;
+    case 'toggleNotificationHistory':
+      deps.toggleNotificationHistory();
+      return;
     case 'markAudioCard':
       await deps.markLastCardAsAudioCard();
       return;