Add mark all as read action to notifications list

Shows a done_all icon button in the AppBar when the New filter is active
and the list is non-empty, calling the notifications/mark_all_as_old endpoint.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/lib/notifications/notification_list.dart

@@ -32,6 +32,20 @@ class _NotificationListState extends State<NotificationList> {
     },
   );
 
+  Future<void> _markAllAsRead(BuildContext context) async {
+    await BackendAPI.instance.markAllNotificationsAsRead();
+    _pagingController.refresh();
+    if (context.mounted) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(
+          content: Text('All notifications marked as read'),
+          behavior: SnackBarBehavior.floating,
+          showCloseIcon: true,
+        ),
+      );
+    }
+  }
+
   Future<bool> _markAsRead(
     BuildContext context,
     oott_model.Notification item,
@@ -102,13 +116,22 @@ class _NotificationListState extends State<NotificationList> {
 
   @override
   Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(title: const Text('Notifications')),
-      body:
     // Paginated list start
-          PagingListener(
+    return PagingListener(
       controller: _pagingController,
-            builder: (context, state, fetchNextPage) => CustomScrollView(
+      builder: (context, state, fetchNextPage) => Scaffold(
+        appBar: AppBar(
+          title: const Text('Notifications'),
+          actions: [
+            if (_filterChoice == 1 && (state.items?.isNotEmpty ?? false))
+              IconButton(
+                onPressed: () => _markAllAsRead(context),
+                icon: const Icon(Icons.done_all),
+                tooltip: 'Mark all as read',
+              ),
+          ],
+        ),
+        body: CustomScrollView(
           slivers: [
             // Filters go here
             SliverToBoxAdapter(

frontend/lib/utils/oott_api.dart

@@ -76,6 +76,11 @@ class BackendAPI {
     await _dio.post('/notifications/$id/mark_as_new');
   }
 
+  Future<void> markAllNotificationsAsRead() async {
+    print('About to call /notifications/mark_all_as_old');
+    await _dio.post('/notifications/mark_all_as_old');
+  }
+
   Future<List<Notification>> listNotifications(bool? isNew, int offset) async {
     print('About to call /notifications');