feat: Flutter 客户端 App + Web UI APK 下载入口

- 新增 Flutter 跨平台客户端项目 (clients/flutter/)
  - 29 个 Dart 文件: 服务层/状态管理/5个页面/BLE配网
  - BLE 蓝牙配网: 扫描设备、写入WiFi凭据、配网状态监听
  - HTTP API 客户端: 覆盖全部端点 (播放/场景/WiFi/视频/配置/文件/插件)
  - WebSocket 实时通信: 事件流 + 自动重连
  - 暗色主题 Material 3 UI, 中文界面
  - Android 配置: minSdkVersion 21, BLE/网络权限
  - PRD 产品需求文档 + 开发任务看板
- Web UI 添加 APK 下载入口 (routes.rs)
  - 下载弹窗 + 二维码 + /download/{filename} 静态文件路由
- BLE 插件增加自动重连循环 (ble/mod.rs)
- BLE 默认设备名修正为 'Showen' (config.rs)

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

clients/flutter/lib/providers/wifi_provider.dart

@@ -0,0 +1,132 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+
+import '../models/wifi_network.dart';
+import '../models/wifi_status.dart';
+import '../services/http_api_service.dart';
+import '../services/web_socket_service.dart';
+
+class WifiProvider extends ChangeNotifier {
+  WifiProvider({
+    required HttpApiService httpApiService,
+    required WebSocketService webSocketService,
+  })  : _httpApiService = httpApiService,
+        _webSocketService = webSocketService {
+    _wifiSubscription = _webSocketService.onWifiUpdate.listen((payload) {
+      _status = WifiStatus.fromJson(payload);
+      notifyListeners();
+    });
+  }
+
+  final HttpApiService _httpApiService;
+  final WebSocketService _webSocketService;
+  late final StreamSubscription<Map<String, dynamic>> _wifiSubscription;
+
+  WifiStatus _status = WifiStatus.disconnected();
+  List<WifiNetwork> _networks = const <WifiNetwork>[];
+  bool _isLoading = false;
+  String? _errorMessage;
+  bool _hotspotEnabled = false;
+
+  WifiStatus get status => _status;
+  List<WifiNetwork> get networks => _networks;
+  bool get isLoading => _isLoading;
+  String? get errorMessage => _errorMessage;
+  bool get hotspotEnabled => _hotspotEnabled;
+
+  Future<void> bootstrap() async {
+    _setLoading(true);
+    try {
+      final results = await Future.wait<dynamic>([
+        _httpApiService.getWifiStatus(),
+        _httpApiService.scanWifi(),
+      ]);
+      _status = results[0] as WifiStatus;
+      _networks = results[1] as List<WifiNetwork>;
+      _errorMessage = null;
+    } catch (error) {
+      _errorMessage = error.toString();
+    } finally {
+      _setLoading(false);
+    }
+  }
+
+  Future<void> refreshStatus() async {
+    try {
+      _status = await _httpApiService.getWifiStatus();
+      notifyListeners();
+    } catch (error) {
+      _errorMessage = error.toString();
+      notifyListeners();
+    }
+  }
+
+  Future<void> scanNetworks() async {
+    _setLoading(true);
+    try {
+      _networks = await _httpApiService.scanWifi();
+      _errorMessage = null;
+    } catch (error) {
+      _errorMessage = error.toString();
+    } finally {
+      _setLoading(false);
+    }
+  }
+
+  Future<void> connect({required String ssid, required String password}) async {
+    _setLoading(true);
+    try {
+      await _httpApiService.connectWifi(ssid, password);
+      await refreshStatus();
+      _hotspotEnabled = false;
+      _errorMessage = null;
+    } catch (error) {
+      _errorMessage = error.toString();
+      notifyListeners();
+    } finally {
+      _setLoading(false);
+    }
+  }
+
+  Future<void> startHotspot({String? ssid, String? password}) async {
+    _setLoading(true);
+    try {
+      await _httpApiService.startAP(ssid, password);
+      _hotspotEnabled = true;
+      _errorMessage = null;
+      notifyListeners();
+    } catch (error) {
+      _errorMessage = error.toString();
+      notifyListeners();
+    } finally {
+      _setLoading(false);
+    }
+  }
+
+  Future<void> stopHotspot() async {
+    _setLoading(true);
+    try {
+      await _httpApiService.stopAP();
+      _hotspotEnabled = false;
+      _errorMessage = null;
+      notifyListeners();
+    } catch (error) {
+      _errorMessage = error.toString();
+      notifyListeners();
+    } finally {
+      _setLoading(false);
+    }
+  }
+
+  void _setLoading(bool value) {
+    _isLoading = value;
+    notifyListeners();
+  }
+
+  @override
+  void dispose() {
+    unawaited(_wifiSubscription.cancel());
+    super.dispose();
+  }
+}