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/services/ble_service.dart

@@ -0,0 +1,215 @@
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:flutter_blue_plus/flutter_blue_plus.dart';
+
+import '../models/ble_models.dart';
+
+class BleService {
+  static final Guid _provisionServiceUuid =
+      Guid('12345678-1234-5678-1234-56789abcdef0');
+  static final Guid _ssidCharacteristicUuid =
+      Guid('12345678-1234-5678-1234-56789abcdef1');
+  static final Guid _passwordCharacteristicUuid =
+      Guid('12345678-1234-5678-1234-56789abcdef2');
+  static final Guid _commandCharacteristicUuid =
+      Guid('12345678-1234-5678-1234-56789abcdef3');
+  static final Guid _statusCharacteristicUuid =
+      Guid('12345678-1234-5678-1234-56789abcdef4');
+
+  BluetoothDevice? _connectedDevice;
+  BluetoothCharacteristic? _ssidCharacteristic;
+  BluetoothCharacteristic? _passwordCharacteristic;
+  BluetoothCharacteristic? _commandCharacteristic;
+  BluetoothCharacteristic? _statusCharacteristic;
+  StreamSubscription<List<ScanResult>>? _scanSubscription;
+
+  Stream<List<BleDevice>> scanForShowenDevices({
+    Duration timeout = const Duration(seconds: 6),
+  }) {
+    final controller = StreamController<List<BleDevice>>();
+    final seen = <String, BleDevice>{};
+
+    unawaited(_scanSubscription?.cancel());
+    _scanSubscription = FlutterBluePlus.scanResults.listen((results) {
+      for (final result in results) {
+        final name = _deviceName(result);
+        if (name.isEmpty || !name.toLowerCase().contains('showen')) {
+          continue;
+        }
+        final id = result.device.remoteId.str;
+        seen[id] = BleDevice(name: name, id: id, rssi: result.rssi);
+      }
+
+      final devices = seen.values.toList(growable: false)
+        ..sort((a, b) => b.rssi.compareTo(a.rssi));
+      if (!controller.isClosed) {
+        controller.add(devices);
+      }
+    });
+
+    unawaited(FlutterBluePlus.startScan(timeout: timeout));
+    Future<void>.delayed(timeout, () async {
+      await FlutterBluePlus.stopScan();
+      if (!controller.isClosed) {
+        await controller.close();
+      }
+    });
+
+    controller.onCancel = () async {
+      await FlutterBluePlus.stopScan();
+      await _scanSubscription?.cancel();
+      _scanSubscription = null;
+    };
+
+    return controller.stream;
+  }
+
+  Future<void> connectToDevice(BleDevice device) async {
+    await disconnect();
+    final bluetoothDevice = BluetoothDevice.fromId(device.id);
+    await bluetoothDevice.connect(timeout: const Duration(seconds: 12));
+    _connectedDevice = bluetoothDevice;
+    await _discoverCharacteristics(bluetoothDevice);
+  }
+
+  Future<Stream<BleStatus>> subscribeToStatus() async {
+    final characteristic = _statusCharacteristic;
+    if (characteristic == null) {
+      return Stream<BleStatus>.value(
+        const BleStatus(
+          ok: false,
+          action: 'status',
+          error: '未发现 BLE 状态特征值',
+        ),
+      );
+    }
+
+    await characteristic.setNotifyValue(true);
+    return characteristic.lastValueStream
+        .where((value) => value.isNotEmpty)
+        .map((value) {
+      final raw = utf8.decode(value, allowMalformed: true);
+      try {
+        return BleStatus.fromRawJson(raw);
+      } catch (_) {
+        return BleStatus(
+          ok: true,
+          action: 'status',
+          state: raw,
+        );
+      }
+    });
+  }
+
+  Future<BleStatus> provisionWifi(
+    String ssid,
+    String password, {
+    Duration timeout = const Duration(seconds: 30),
+  }) async {
+    final ssidChar = _ssidCharacteristic;
+    final passwordChar = _passwordCharacteristic;
+    final command = _commandCharacteristic;
+
+    if (_connectedDevice == null) {
+      throw StateError('未连接 BLE 设备');
+    }
+    if (ssidChar == null || passwordChar == null || command == null) {
+      throw StateError('未发现 BLE 配网特征值');
+    }
+
+    final statusStream = await subscribeToStatus();
+    final completer = Completer<BleStatus>();
+    late final StreamSubscription<BleStatus> subscription;
+    subscription = statusStream.listen((status) {
+      if (!status.isQueued && !completer.isCompleted) {
+        completer.complete(status);
+      }
+    }, onError: (Object error, StackTrace stackTrace) {
+      if (!completer.isCompleted) {
+        completer.completeError(error, stackTrace);
+      }
+    });
+
+    await ssidChar.write(
+      utf8.encode(ssid),
+      withoutResponse: ssidChar.properties.writeWithoutResponse,
+    );
+    await passwordChar.write(
+      utf8.encode(password),
+      withoutResponse: passwordChar.properties.writeWithoutResponse,
+    );
+    await command.write(
+      utf8.encode('connect'),
+      withoutResponse: command.properties.writeWithoutResponse,
+    );
+
+    try {
+      return await completer.future.timeout(timeout);
+    } finally {
+      await subscription.cancel();
+    }
+  }
+
+  Future<void> disconnect() async {
+    await _scanSubscription?.cancel();
+    _scanSubscription = null;
+
+    final device = _connectedDevice;
+    _connectedDevice = null;
+    _ssidCharacteristic = null;
+    _passwordCharacteristic = null;
+    _commandCharacteristic = null;
+    _statusCharacteristic = null;
+
+    if (device != null) {
+      await device.disconnect();
+    }
+  }
+
+  Future<void> dispose() => disconnect();
+
+  Future<void> _discoverCharacteristics(BluetoothDevice device) async {
+    final services = await device.discoverServices();
+
+    BluetoothCharacteristic? ssid;
+    BluetoothCharacteristic? password;
+    BluetoothCharacteristic? command;
+    BluetoothCharacteristic? status;
+
+    for (final service in services) {
+      final shouldInspect = service.uuid == _provisionServiceUuid ||
+          services.length == 1 ||
+          service.characteristics.isNotEmpty;
+      if (!shouldInspect) {
+        continue;
+      }
+
+      for (final characteristic in service.characteristics) {
+        if (characteristic.uuid == _ssidCharacteristicUuid) {
+          ssid = characteristic;
+        } else if (characteristic.uuid == _passwordCharacteristicUuid) {
+          password = characteristic;
+        } else if (characteristic.uuid == _commandCharacteristicUuid) {
+          command = characteristic;
+        } else if (characteristic.uuid == _statusCharacteristicUuid) {
+          status = characteristic;
+        }
+      }
+    }
+
+    _ssidCharacteristic = ssid;
+    _passwordCharacteristic = password;
+    _commandCharacteristic = command;
+    _statusCharacteristic = status;
+  }
+
+  String _deviceName(ScanResult result) {
+    final platformName = result.device.platformName.trim();
+    if (platformName.isNotEmpty) {
+      return platformName;
+    }
+    final advertisedName = result.advertisementData.advName.trim();
+    return advertisedName;
+  }
+}