delete CloudKit and added BalanceFlutter

BalanceFlutter/lib/services/runtime_lock.dart

@@ -0,0 +1,36 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+import 'runtime_lock_stub.dart'
+    if (dart.library.js_interop) 'runtime_lock_web.dart'
+    as browser;
+
+/// Native Android lock shared by the UI engine and WorkManager headless engines.
+/// Callers must hold it over reloading preferences/session, ledger IO and sync.
+class RuntimeLock {
+  static const _channel = MethodChannel('balance/runtime');
+  final _browserLock = browser.BrowserRuntimeLock();
+  String? _token;
+  bool get _android =>
+      !kIsWeb && defaultTargetPlatform == TargetPlatform.android;
+
+  Future<void> acquire() async {
+    if (kIsWeb) return _browserLock.acquire();
+    if (!_android) return;
+    if (_token != null) throw StateError('Ledger lock is already held');
+    final token = await _channel.invokeMethod<String>('acquireLock');
+    if (token == null || token.isEmpty) {
+      throw StateError('Native ledger lock returned no ownership token');
+    }
+    _token = token;
+  }
+
+  Future<void> release() async {
+    if (kIsWeb) return _browserLock.release();
+    if (!_android) return;
+    final token = _token;
+    if (token == null) throw StateError('Ledger lock is not held');
+    await _channel.invokeMethod<void>('releaseLock', {'token': token});
+    _token = null;
+  }
+}