fix(genex-mobile): 升级 fluwx 3.x → 5.x，适配新版 API

fluwx 3.x 不含 Android namespace，导致新版 AGP 构建失败。
升级至 5.x 并迁移 API：
- registerWxApi → Fluwx().registerApi()
- weChatResponseEventHandler → fluwx.addSubscriber()
- sendWeChatAuth → fluwx.authBy(NormalAuth)
- isWeChatInstalled → fluwx.isWeChatInstalled
- WXAuthResp → WeChatAuthResponse

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

frontend/genex-mobile/lib/features/auth/presentation/pages/welcome_page.dart

@@ -28,7 +28,7 @@ import '../../../../core/services/auth_service.dart';
 ///   flutter build apk --dart-define=WECHAT_APP_ID=wx0000000000000000
 ///
 /// ── 登录流程（各平台）────────────────────────────────────
-///   微信:   fluwx.sendWeChatAuth → WXAuthResp(code) → POST /auth/wechat
+///   微信:   fluwx.authBy(NormalAuth) → WeChatAuthResponse(code) → POST /auth/wechat
 ///   支付宝: tobias.aliPayAuth → Map(result 含 auth_code) → POST /auth/alipay
 ///   Google: google_sign_in.signIn → GoogleSignInAuthentication.idToken → POST /auth/google
 ///   Apple:  sign_in_with_apple.getAppleIDCredential → identityToken → POST /auth/apple
@@ -50,13 +50,16 @@ class _WelcomePageState extends State<WelcomePage> {
   // 'profile': 获取用户显示名和头像 URL
   final _googleSignIn = GoogleSignIn(scopes: ['email', 'profile']);
 
+  // fluwx 5.x 使用实例方式调用，registerApi 在 main.dart 中已完成
+  final _fluwx = Fluwx();
+
   @override
   void initState() {
     super.initState();
     // 监听微信授权回调（用户授权后，微信 App 返回 code）
-    weChatResponseEventHandler.distinct().listen((res) {
-      if (res is WXAuthResp && mounted) {
-        _handleWechatAuthResp(res);
+    _fluwx.addSubscriber((response) {
+      if (response is WeChatAuthResponse && mounted) {
+        _handleWechatAuthResp(response);
       }
     });
   }
@@ -64,7 +67,7 @@ class _WelcomePageState extends State<WelcomePage> {
   // ── 微信 ─────────────────────────────────────────────────────────────────
 
   Future<void> _onWechatTap() async {
-    final installed = await isWeChatInstalled;
+    final installed = await _fluwx.isWeChatInstalled;
     if (!installed) {
       if (mounted) {
         ScaffoldMessenger.of(context).showSnackBar(
@@ -74,13 +77,13 @@ class _WelcomePageState extends State<WelcomePage> {
       return;
     }
     setState(() => _wechatLoading = true);
-    await sendWeChatAuth(scope: 'snsapi_userinfo', state: 'genex_login');
-    // 授权结果通过 weChatResponseEventHandler 异步回调
+    await _fluwx.authBy(which: NormalAuth(scope: 'snsapi_userinfo', state: 'genex_login'));
+    // 授权结果通过 addSubscriber 异步回调
   }
 
-  Future<void> _handleWechatAuthResp(WXAuthResp resp) async {
+  Future<void> _handleWechatAuthResp(WeChatAuthResponse resp) async {
     setState(() => _wechatLoading = false);
-    if (resp.errCode != 0 || resp.code == null) return;
+    if ((resp.errCode ?? -1) != 0 || resp.code == null) return;
     try {
       await AuthService.instance.loginByWechat(code: resp.code!);
       if (mounted) Navigator.pushReplacementNamed(context, '/main');

frontend/genex-mobile/lib/main.dart

@@ -56,7 +56,7 @@ Future<void> main() async {
   //   详见: https://developers.weixin.qq.com/doc/oplatform/Mobile_App/Universal_Links/Universal_Links.html
   const wechatAppId = String.fromEnvironment('WECHAT_APP_ID', defaultValue: '');
   if (wechatAppId.isNotEmpty) {
-    await registerWxApi(appId: wechatAppId, universalLink: 'https://www.gogenex.com/wechat/');
+    await Fluwx().registerApi(appId: wechatAppId, universalLink: 'https://www.gogenex.com/wechat/');
   }
   // ─────────────────────────────────────────────────────────────────────
 

frontend/genex-mobile/pubspec.yaml

@@ -26,7 +26,7 @@ dependencies:
   qr_flutter: ^4.1.0
   share_plus: ^10.0.2
   flutter_secure_storage: ^9.2.2
-  fluwx: ^3.10.0
+  fluwx: ^5.0.0
   tobias: ^3.0.0
   google_sign_in: ^6.2.1
   sign_in_with_apple: ^6.1.0