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/main/runtime/update/update-notifications.ts

@@ -1,6 +1,9 @@
 import type { UpdateNotificationType } from '../../../types/config';
 import type { OverlayNotificationPayload } from '../../../types/notification';
 
+export const UPDATE_AVAILABLE_NOTIFICATION_ID = 'subminer-update-available';
+export const INSTALL_UPDATE_ACTION_ID = 'install-update';
+
 export interface UpdateNotificationDeps {
   showSystemNotification: (title: string, body: string) => void;
   showOverlayNotification: (payload: OverlayNotificationPayload) => void;
@@ -17,9 +20,12 @@ export async function notifyUpdateAvailable(
   const message = `SubMiner v${options.version} is available`;
   if (options.notificationType === 'overlay' || options.notificationType === 'both') {
     deps.showOverlayNotification({
+      id: UPDATE_AVAILABLE_NOTIFICATION_ID,
       title: 'SubMiner update available',
       body: message,
       variant: 'info',
+      persistent: true,
+      actions: [{ id: INSTALL_UPDATE_ACTION_ID, label: 'Update' }],
     });
   }
   if (options.notificationType === 'osd' || options.notificationType === 'osd-system') {