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/components/NotificationBell.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect } from 'react';
+import React, { useState, useEffect, useRef } from 'react';
 import { Badge, Popover, Button, List, Typography, Empty } from 'antd';
 import { BellOutlined } from '@ant-design/icons';
 import { useNavigate } from 'react-router-dom';
@@ -56,7 +56,10 @@ const NotificationBell: React.FC = () => {
       setUnreadCount(data.count);
     } catch { /* ignore */ }
   };
+  const openRef = useRef(open);
+  openRef.current = open;
 
+  // SSE connection — decoupled from popover open state
   useEffect(() => {
     fetchUnread();
     const token = localStorage.getItem('token');
@@ -66,16 +69,15 @@ const NotificationBell: React.FC = () => {
       try {
         JSON.parse(event.data);
         setUnreadCount((c) => c + 1);
-        if (open) fetchNotifications();
+        if (openRef.current) fetchNotifications();
       } catch { /* ignore */ }
     };
     es.onerror = () => {
       es.close();
-      const interval = setInterval(fetchUnread, 60_000);
-      return () => clearInterval(interval);
+      setInterval(fetchUnread, 60_000);
     };
     return () => es.close();
-  }, [open]);
+  }, []);
 
   const handleOpen = (visible: boolean) => {
     setOpen(visible);