Offline tab as Files view, automatic background sync, sync notifications

- Offline tab is now FilesView(offline: true) over a FolderBrowser interface
  (FilesController / OfflineController) sharing controls, tiles, thumbnails
- Synced files follow the Files Cache rule (default: refresh every 15 min):
  per-account WorkManager jobs, in-app timer, resume and pull triggers;
  root-etag shortcut skips full walks when nothing changed
- Single sync at a time (shared lock); logging out stops that account's sync
- Sync safety: PROPFIND failures skip the path instead of deleting local files
- Mirror empty folders and remove deleted ones; drop synced paths deleted on
  the server; missing local files are re-downloaded
- Notifications: silent per-account sync notifications, "Background sync
  notifications" setting, audible upload/download completion
- Files refresh in place (no spinner flash); retry after network returns
- Fix sync badges not updating (shared native status stream), "Sync off" on
  launch (eager providers), Files Cache section moved under Device Sync

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

test/widget_test.dart

@@ -4,9 +4,11 @@ import 'package:google_fonts/google_fonts.dart';
 import 'package:provider/provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:noo/main.dart';
+import 'package:noo/providers/connectivity_controller.dart';
 import 'package:noo/providers/favorites_controller.dart';
 import 'package:noo/providers/files_controller.dart';
 import 'package:noo/providers/item_operations.dart';
+import 'package:noo/providers/offline_controller.dart';
 import 'package:noo/providers/photos_controller.dart';
 import 'package:noo/providers/pick_controller.dart';
 import 'package:noo/providers/recent_controller.dart';
@@ -20,6 +22,12 @@ void main() {
   const secureStorageChannel = MethodChannel(
     'plugins.it_nomads.com/flutter_secure_storage',
   );
+  const connectivityChannel = MethodChannel(
+    'dev.fluttercommunity.plus/connectivity',
+  );
+  const connectivityStatusChannel = EventChannel(
+    'dev.fluttercommunity.plus/connectivity_status',
+  );
 
   setUpAll(() {
     GoogleFonts.config.allowRuntimeFetching = false;
@@ -29,10 +37,22 @@ void main() {
           if (call.method == 'readAll') return <String, String>{};
           return null;
         });
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(connectivityChannel, (call) async {
+          if (call.method == 'check') return <String>['wifi'];
+          return null;
+        });
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockStreamHandler(
+          connectivityStatusChannel,
+          MockStreamHandler.inline(
+            onListen: (arguments, events) {},
+          ),
+        );
   });
 
   test('SessionController initializes unauthenticated', () {
-    final session = SessionController();
+    final session = SessionController(ConnectivityController());
     expect(session.isLoggedIn, false);
   });
 
@@ -43,13 +63,17 @@ void main() {
       MultiProvider(
         // Mirrors main.dart's own provider order/wiring.
         providers: [
-          ChangeNotifierProvider(create: (_) => SessionController()),
+          ChangeNotifierProvider(create: (_) => ConnectivityController()),
+          ChangeNotifierProvider(
+            create: (context) => SessionController(context.read()),
+          ),
           ChangeNotifierProvider(create: (_) => SettingsController()),
           ChangeNotifierProvider(
-            create: (context) => SyncStatusController(context.read()),
+            create: (context) => FilesController(context.read()),
           ),
           ChangeNotifierProvider(
-            create: (context) => FilesController(context.read()),
+            create: (context) =>
+                SyncStatusController(context.read(), context.read()),
           ),
           ChangeNotifierProvider(
             create: (context) =>
@@ -71,6 +95,10 @@ void main() {
           ChangeNotifierProvider(
             create: (context) => PickController(context.read()),
           ),
+          ChangeNotifierProvider(
+            create: (context) =>
+                OfflineController(context.read(), context.read()),
+          ),
           Provider(
             create: (context) => ItemOperations(
               session: context.read(),