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/config/settings/registry.ts

@@ -582,6 +582,7 @@ function subsectionForPath(path: string): string | undefined {
     if (
       leaf === 'toggleVisibleOverlayGlobal' ||
       leaf === 'toggleSubtitleSidebar' ||
+      leaf === 'toggleNotificationHistory' ||
       leaf === 'toggleSecondarySub' ||
       leaf === 'toggleStatsOverlay' ||
       leaf === 'markWatched'