fix+build(client/windows): 复查修缮——一键构建脚本 + 修 README dart-define 漏项 + 清 lint

- 新增 client/windows/build.ps1：拉内核→带 --dart-define 构建→出安装包一键串联，
  规避 Release 漏 --dart-define 导致默认连 localhost、登录「网络请求失败」的坑。
- README：Release 命令补回 --dart-define 并加显式警告，指向一键脚本。
- 清 4 个 lint warning：desktop_vpn_bridge 多余 cast→pattern match、去多余非空断言；
  nav_sidebar 删未用 import；vpn_bridge_mock 加 killSwitchEnabled getter。
- 同步 window_manager/tray_manager/screen_retriever 插件注册生成文件(win+macos)。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/bridge/desktop_vpn_bridge.dart

@@ -213,8 +213,8 @@ class DesktopVpnBridge implements VpnBridge {
     _reconnectTimer = null;
     _kernelStatusSub?.cancel();
     _kernelStatusSub = null;
-    if (_kernel is DesktopKernelProcess) {
-      (_kernel as DesktopKernelProcess).dispose();
+    if (_kernel case final DesktopKernelProcess k) {
+      k.dispose();
     }
   }
 
@@ -350,7 +350,7 @@ class DesktopVpnBridge implements VpnBridge {
 
   Future<Directory> _resolveConfigDir() async {
     if (_configDirOverride != null) {
-      return Directory(_configDirOverride!);
+      return Directory(_configDirOverride);
     }
     return _defaultConfigDir();
   }

client/lib/bridge/vpn_bridge_mock.dart

@@ -121,6 +121,9 @@ class VpnBridgeMock implements VpnBridge {
     _killSwitch = on;
   }
 
+  /// 测试可读：mock 记录的 kill-switch 状态。
+  bool get killSwitchEnabled => _killSwitch;
+
   @override
   Stream<VpnStatus> get statusStream => _statusCtrl.stream;
 

client/lib/widgets/nav_sidebar.dart

@@ -8,7 +8,6 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../pangolin_theme.dart';
 import '../state/app_providers.dart';
 import '../state/navigation_provider.dart';
-import 'pangolin_icons.dart';
 import 'pangolin_logo.dart';
 import 'plan_badge_card.dart';