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/admin/src/hooks/useNotifications.ts

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect, useCallback, useRef } from 'react';
 import api from '../api';
 
 interface Notification {
@@ -41,16 +41,18 @@ export function useNotifications() {
       }
     };
 
+    const pollRef = { current: undefined as number | undefined };
+
     es.onerror = () => {
       es.close();
-      const interval = setInterval(() => {
+      pollRef.current = setInterval(() => {
         fetchUnreadCount();
       }, 60_000);
-      return () => clearInterval(interval);
     };
 
     return () => {
       es.close();
+      if (pollRef.current !== undefined) clearInterval(pollRef.current);
     };
   }, [fetchUnreadCount]);