feat(bridge): 桥接 API 面 Channel 契约 + 三端原生骨架 [tsk_iP5-_Ztq5THx]

MethodChannel pangolin/vpn (start/stop/getStatus/selectOutbound/
getActiveOutbound/setKillSwitch) + 双 EventChannel (status/stats)
契约定义在 lib/bridge/vpn_bridge.dart 头部注释冻结。

- Dart: VpnBridge 抽象接口 + VpnNativeBridge 原生实现 + VpnBridgeMock
  假内核（含 connectDelay/statsInterval 可配参数）
- Dart 桌面: kernel_process.dart KernelProcess/ClashApiClient 接口骨架
- Android: PangolinVpnService (VpnService 骨架 + 前台通知占位) +
  VpnEventBus 解耦总线 + MainActivity MethodChannel/EventChannel 注册
- iOS: PacketTunnelProvider (NEPacketTunnelProvider 骨架) + VpnManager
  (NETunnelProviderManager + NEVPNStatus 订阅) + AppDelegate 通道注册
  + Xcode project.pbxproj 添加 PacketTunnel extension target
- Widget: VpnStatus enum 迁移至 bridge/vpn_bridge.dart (+error 态)，
  connect_button/home_shell 更新穷举匹配
- Test: test/bridge/vpn_bridge_mock_test.dart 覆盖 start→connecting→on
  →stop→off 序列、stats 周期推帧、selectOutbound 重连序列、schema 回测

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

client/lib/bridge/vpn_bridge_mock.dart

@@ -0,0 +1,137 @@
+// vpn_bridge_mock.dart — 假内核实现，供 UI 层先行联调
+//
+// 行为：
+//   start()  → 立即 emit connecting，[connectDelay] 后 emit on，启动统计计时器
+//   stop()   → 立即 emit off，停止统计计时器
+//   stats    → on 状态下按 [statsInterval] 周期推假数据帧
+//
+// 用法示例（UI 联调）：
+//   final bridge = VpnBridgeMock();
+//
+// 用法示例（测试）：
+//   final bridge = VpnBridgeMock(
+//     connectDelay:  Duration(milliseconds: 50),
+//     statsInterval: Duration(milliseconds: 50),
+//   );
+
+import 'dart:async';
+import 'dart:math';
+import 'vpn_bridge.dart';
+
+class VpnBridgeMock implements VpnBridge {
+  VpnBridgeMock({
+    this.connectDelay = const Duration(milliseconds: 1500),
+    this.statsInterval = const Duration(seconds: 1),
+  });
+
+  final Duration connectDelay;
+  final Duration statsInterval;
+
+  // 内部状态
+  VpnStatus _status = VpnStatus.off;
+  String _activeOutbound = 'auto';
+  bool _killSwitch = false;
+
+  final _statusCtrl = StreamController<VpnStatus>.broadcast();
+  final _statsCtrl = StreamController<VpnStatsEvent>.broadcast();
+
+  Timer? _connectTimer;
+  Timer? _statsTimer;
+
+  int _tickCount = 0;
+  final _rng = Random();
+
+  // ── helpers ───────────────────────────────────────────────────
+
+  void _emitStatus(VpnStatus s) {
+    _status = s;
+    if (!_statusCtrl.isClosed) _statusCtrl.add(s);
+  }
+
+  void _startStats() {
+    _tickCount = 0;
+    _statsTimer?.cancel();
+    _statsTimer = Timer.periodic(statsInterval, (_) {
+      _tickCount++;
+      if (!_statsCtrl.isClosed) _statsCtrl.add(_fakeTick(_tickCount));
+    });
+  }
+
+  VpnStatsEvent _fakeTick(int t) {
+    // 模拟稳定带宽 + 微抖动
+    final upSpeed = 10240.0 + _rng.nextDouble() * 2048;
+    final downSpeed = 51200.0 + _rng.nextDouble() * 8192;
+    return VpnStatsEvent(
+      uploadBytes: (upSpeed * t * statsInterval.inMilliseconds / 1000).round(),
+      downloadBytes: (downSpeed * t * statsInterval.inMilliseconds / 1000).round(),
+      uploadSpeed: upSpeed,
+      downloadSpeed: downSpeed,
+      urltestResults: const [
+        UrltestResult(tag: 'hk-01', delayMs: 18),
+        UrltestResult(tag: 'jp-01', delayMs: 32),
+        UrltestResult(tag: 'sg-01', delayMs: 54),
+      ],
+    );
+  }
+
+  // ── VpnBridge methods ─────────────────────────────────────────
+
+  @override
+  Future<void> start(String configJson) async {
+    _connectTimer?.cancel();
+    _statsTimer?.cancel();
+    _emitStatus(VpnStatus.connecting);
+    _connectTimer = Timer(connectDelay, () {
+      _emitStatus(VpnStatus.on);
+      _startStats();
+    });
+  }
+
+  @override
+  Future<void> stop() async {
+    _connectTimer?.cancel();
+    _statsTimer?.cancel();
+    _connectTimer = null;
+    _statsTimer = null;
+    _emitStatus(VpnStatus.off);
+  }
+
+  @override
+  Future<VpnStatus> getStatus() async => _status;
+
+  @override
+  Future<void> selectOutbound(String tag) async {
+    _activeOutbound = tag;
+    // 切换出口时模拟短暂重连
+    if (_status == VpnStatus.on) {
+      _statsTimer?.cancel();
+      _emitStatus(VpnStatus.connecting);
+      _connectTimer = Timer(connectDelay ~/ 2, () {
+        _emitStatus(VpnStatus.on);
+        _startStats();
+      });
+    }
+  }
+
+  @override
+  Future<String> getActiveOutbound() async => _activeOutbound;
+
+  @override
+  Future<void> setKillSwitch({required bool on}) async {
+    _killSwitch = on;
+  }
+
+  @override
+  Stream<VpnStatus> get statusStream => _statusCtrl.stream;
+
+  @override
+  Stream<VpnStatsEvent> get statsStream => _statsCtrl.stream;
+
+  @override
+  void dispose() {
+    _connectTimer?.cancel();
+    _statsTimer?.cancel();
+    _statusCtrl.close();
+    _statsCtrl.close();
+  }
+}