fix: apply code review fixes — double layout, SSE leaks, interval leak, conflict values

- App.tsx: remove double-wrapped MainLayout from /notifications route
- NotificationBell.tsx: decouple SSE from popover open state using ref
- useNotifications.ts: fix interval leak in onerror via ref in cleanup
- notifications.controller.ts: unsubscribe on req.on('close') for SSE Subject
- schedules.controller.ts: use existing schedule values in conflict catch

apps/server/src/notifications/notifications.controller.ts

@@ -48,6 +48,9 @@ export class NotificationsController {
   @Sse('stream')
   stream(@Req() req: AuthenticatedRequest): Observable<MessageEvent> {
     const userId = req.user.id;
+    req.on('close', () => {
+      this.service.unsubscribe(userId);
+    });
     return this.service.subscribe(userId).pipe(
       map((notification) => ({
         data: JSON.stringify({