Dedupe native transfer/notification code and split ServerProvider into focused controllers

Consolidates duplicated GET/PUT/notification-channel logic across
DownloadService/ShareUploadService/SyncEngine into shared Kotlin helpers,
gives upload/download real batch queueing instead of dropping a second
concurrent batch, and dedupes repeated Dart channel-argument boilerplate.

Replaces the 2300+ line ServerProvider god object with ten focused
ChangeNotifiers (SessionController, SettingsController, FilesController,
PhotosController, FavoritesController, TrashController, SharesController,
RecentController, SyncStatusController, PickController) plus ItemOperations,
a plain coordinator for cross-domain item mutations - fixing the coupling
where device-sync status, per-tab data, and global UI prefs all lived in
one object. Updates every view/widget call site accordingly and refreshes
the architecture/server/standards/styling docs to match.

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

test/widget_test.dart

@@ -4,7 +4,17 @@ 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/server_provider.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/photos_controller.dart';
+import 'package:noo/providers/pick_controller.dart';
+import 'package:noo/providers/recent_controller.dart';
+import 'package:noo/providers/session_controller.dart';
+import 'package:noo/providers/settings_controller.dart';
+import 'package:noo/providers/shares_controller.dart';
+import 'package:noo/providers/sync_status_controller.dart';
+import 'package:noo/providers/trash_controller.dart';
 
 void main() {
   const secureStorageChannel = MethodChannel(
@@ -21,20 +31,55 @@ void main() {
         });
   });
 
-  test('ServerProvider initializes unauthenticated', () {
-    final provider = ServerProvider();
-    expect(provider.isLoggedIn, false);
-    expect(provider.items.isEmpty, true);
+  test('SessionController initializes unauthenticated', () {
+    final session = SessionController();
+    expect(session.isLoggedIn, false);
   });
 
   testWidgets('App renders LoginView when not logged in', (
     WidgetTester tester,
   ) async {
-    final provider = ServerProvider();
-
     await tester.pumpWidget(
-      ChangeNotifierProvider.value(
-        value: provider,
+      MultiProvider(
+        // Mirrors main.dart's own provider order/wiring.
+        providers: [
+          ChangeNotifierProvider(create: (_) => SessionController()),
+          ChangeNotifierProvider(create: (_) => SettingsController()),
+          ChangeNotifierProvider(
+            create: (context) => SyncStatusController(context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) => FilesController(context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) =>
+                PhotosController(context.read(), context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) =>
+                FavoritesController(context.read(), context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) => TrashController(context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) => SharesController(context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) => RecentController(context.read()),
+          ),
+          ChangeNotifierProvider(
+            create: (context) => PickController(context.read()),
+          ),
+          Provider(
+            create: (context) => ItemOperations(
+              session: context.read(),
+              files: context.read(),
+              photos: context.read(),
+              favorites: context.read(),
+            ),
+          ),
+        ],
         child: const NextcloudApp(),
       ),
     );