merge: maestro/tsk_iP5-_Ztq5THx [桥接 API 面 Channel 契约 + 三端原生骨架] [tsk_rcNKc3GQHBUd]

合并冲突补救：原分支从 merge base 7871512 分叉，仅修改 client/ 目录，
与 main 新增的 server/(apierr/idgen/CONVENTIONS.md) 完全不重叠，
无真实文件冲突，手动应用 feature branch 的全部 client/ 改动。

client 侧新增：
- lib/bridge/vpn_bridge.dart      — Dart↔原生通道契约（冻结）
- lib/bridge/vpn_bridge_mock.dart — 假内核，UI 联调用
- lib/bridge/kernel_process.dart  — 桌面子进程管理接口
- ios/PacketTunnel/{Info.plist,PacketTunnelProvider.swift} — NEPacketTunnel 骨架
- ios/Runner/VpnManager.swift     — NETunnelProviderManager 封装
- android/.../PangolinVpnService.kt — VpnService 骨架
- android/.../VpnEventBus.kt      — Application 级状态总线
- test/bridge/vpn_bridge_mock_test.dart — 桥接层单元测试

client 侧修改：
- android/.../MainActivity.kt    — 注册三通道（MethodChannel + 2×EventChannel）
- android/.../AndroidManifest.xml — 声明 FOREGROUND_SERVICE + PangolinVpnService
- ios/Runner/AppDelegate.swift   — 注册通道 + VpnManager 初始化
- ios/Runner/Info.plist          — 新增 NSVPNUsageDescription
- ios/Runner.xcodeproj/project.pbxproj — 添加 PacketTunnel extension target
- lib/widgets/connect_button.dart — VpnStatus 迁移到 bridge/vpn_bridge.dart
- lib/widgets/home_shell.dart    — error 状态 UI 分支补全

client/ios/Runner/AppDelegate.swift

@@ -1,13 +1,98 @@
+// AppDelegate.swift — Flutter ↔ 原生通道注册
+//
+// 通道契约（见 lib/bridge/vpn_bridge.dart 头部注释）：
+//   MethodChannel  : pangolin/vpn
+//   EventChannel   : pangolin/vpn/status  → VpnStatusStreamHandler
+//   EventChannel   : pangolin/vpn/stats   → VpnStatsStreamHandler
+//
+// VpnManager.shared 持有 NETunnelProviderManager 与 NEVPNStatus 订阅。
+
 import UIKit
 import Flutter
+import NetworkExtension
 
 @UIApplicationMain
 @objc class AppDelegate: FlutterAppDelegate {
-  override func application(
-    _ application: UIApplication,
-    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
-  ) -> Bool {
-    GeneratedPluginRegistrant.register(with: self)
-    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
-  }
+
+    override func application(
+        _ application: UIApplication,
+        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
+    ) -> Bool {
+        GeneratedPluginRegistrant.register(with: self)
+
+        guard let controller = window?.rootViewController as? FlutterViewController else {
+            return super.application(application, didFinishLaunchingWithOptions: launchOptions)
+        }
+        let messenger = controller.binaryMessenger
+
+        // ── MethodChannel ────────────────────────────────────────
+        let vpnChannel = FlutterMethodChannel(name: "pangolin/vpn", binaryMessenger: messenger)
+        vpnChannel.setMethodCallHandler { [weak self] call, result in
+            self?.handleVpnMethod(call: call, result: result)
+        }
+
+        // ── EventChannel: status ─────────────────────────────────
+        FlutterEventChannel(name: "pangolin/vpn/status", binaryMessenger: messenger)
+            .setStreamHandler(VpnStatusStreamHandler.shared)
+
+        // ── EventChannel: stats ──────────────────────────────────
+        FlutterEventChannel(name: "pangolin/vpn/stats", binaryMessenger: messenger)
+            .setStreamHandler(VpnStatsStreamHandler.shared)
+
+        // 预加载 VPN 偏好设置（首次为空，静默失败）
+        VpnManager.shared.loadFromPreferences { error in
+            if let error = error {
+                NSLog("VpnManager: loadFromPreferences error: %@", error.localizedDescription)
+            }
+        }
+
+        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
+    }
+
+    // ── MethodChannel handler ─────────────────────────────────────
+
+    private func handleVpnMethod(call: FlutterMethodCall, result: @escaping FlutterResult) {
+        switch call.method {
+
+        case "start":
+            let configJson = call.arguments as? String ?? "{}"
+            VpnManager.shared.start(configJson: configJson) { error in
+                if let error = error {
+                    result(FlutterError(
+                        code: "START_FAILED",
+                        message: error.localizedDescription,
+                        details: nil
+                    ))
+                } else {
+                    result(nil)
+                }
+            }
+
+        case "stop":
+            VpnManager.shared.stop()
+            result(nil)
+
+        case "getStatus":
+            result(VpnManager.shared.statusString)
+
+        case "selectOutbound":
+            let tag = call.arguments as? String ?? "auto"
+            NSLog("VPN: selectOutbound tag=%@", tag)
+            // TODO(11F): sendProviderMessage → PacketTunnelProvider outbound selector
+            result(nil)
+
+        case "getActiveOutbound":
+            // TODO(11F): query from PacketTunnelProvider via sendProviderMessage
+            result("auto")
+
+        case "setKillSwitch":
+            let on = call.arguments as? Bool ?? false
+            NSLog("VPN: setKillSwitch on=%d", on ? 1 : 0)
+            // TODO(11F): 通过 include/excludeRoutes 实现 Kill Switch
+            result(nil)
+
+        default:
+            result(FlutterMethodNotImplemented)
+        }
+    }
 }