fix: Notification auto-dismiss not working due to stale closure

The removeNotification function was using a stale reference to the
notifications array from the closure scope, causing the setTimeout
callback to filter against an outdated state.

Changed to use functional update pattern (prev => prev.filter(...))
which correctly references the current state when the timeout fires.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

admin/inertia/providers/NotificationProvider.tsx

@@ -22,7 +22,7 @@ const NotificationsProvider = ({ children }: { children: React.ReactNode }) => {
   }
 
   const removeNotification = (id: string) => {
-    setNotifications(notifications.filter((n) => n.id !== id))
+    setNotifications((prev) => prev.filter((n) => n.id !== id))
   }
 
   const removeAllNotifications = () => {