delete CloudKit and added BalanceFlutter

BalanceFlutter/lib/services/runtime_lock_web.dart

@@ -0,0 +1,96 @@
+import 'dart:async';
+import 'dart:js_interop';
+
+@JS('isSecureContext')
+external bool get _secureContext;
+
+@JS('navigator.locks')
+external JSObject? get _navigatorLocks;
+
+extension type _LockManager(JSObject _) implements JSObject {
+  external JSPromise<JSAny?> request(JSString name, JSFunction callback);
+}
+
+/// Holds the origin-wide Web Lock until release, including IndexedDB commits
+/// and rotated refresh-token persistence. Browser teardown releases the lock.
+class BrowserRuntimeLock {
+  bool _waiting = false;
+  Completer<JSAny?>? _release;
+  Future<JSAny?>? _request;
+
+  Future<void> acquire() async {
+    if (_waiting || _release != null) {
+      throw StateError('Browser ledger lock is already held or pending');
+    }
+    if (!_secureContext) {
+      throw StateError(
+        'Для безопасного хранения данных в нескольких вкладках требуется HTTPS '
+        '(или localhost). Откройте приложение по защищённому адресу.',
+      );
+    }
+    final manager = _navigatorLocks;
+    if (manager == null) {
+      throw StateError(
+        'Браузер не поддерживает Web Locks API. Обновите браузер: '
+        'без блокировки вкладок безопасная синхронизация недоступна.',
+      );
+    }
+    final ready = Completer<void>();
+    final release = Completer<JSAny?>();
+    _waiting = true;
+    try {
+      final request = _LockManager(manager)
+          .request(
+            'balance-ledger-v1'.toJS,
+            ((JSAny? lock) {
+              _waiting = false;
+              _release = release;
+              ready.complete();
+              return release.future.toJS;
+            }).toJS,
+          )
+          .toDart;
+      _request = request;
+      // A rejected request must wake an acquiring caller, not leave it waiting
+      // forever. Keep a rejection handler attached even before release awaits it.
+      unawaited(
+        request.then<void>(
+          (_) {
+            if (!ready.isCompleted) {
+              ready.completeError(
+                StateError('Browser ledger lock was not granted'),
+              );
+            }
+          },
+          onError: (Object error, StackTrace stack) {
+            if (!ready.isCompleted) {
+              ready.completeError(
+                StateError('Не удалось получить блокировку данных браузера'),
+                stack,
+              );
+            }
+          },
+        ),
+      );
+      await ready.future;
+    } catch (_) {
+      _waiting = false;
+      _release = null;
+      _request = null;
+      rethrow;
+    }
+  }
+
+  Future<void> release() async {
+    final release = _release;
+    if (release == null) throw StateError('Browser ledger lock is not held');
+    release.complete(null);
+    try {
+      // Resolves only after navigator.locks has actually released ownership.
+      await _request;
+    } finally {
+      _release = null;
+      _request = null;
+    }
+  }
+}