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/widgets/control_button.dart

@@ -0,0 +1,46 @@
+import 'package:flutter/material.dart';
+
+import '../theme/app_colors.dart';
+
+class ControlButton extends StatelessWidget {
+  const ControlButton({
+    required this.label,
+    required this.icon,
+    required this.onPressed,
+    this.isFilled = true,
+    super.key,
+  });
+
+  final String label;
+  final IconData icon;
+  final VoidCallback? onPressed;
+  final bool isFilled;
+
+  @override
+  Widget build(BuildContext context) {
+    if (isFilled) {
+      return DecoratedBox(
+        decoration: BoxDecoration(
+          gradient: AppColors.primaryGradient,
+          borderRadius: BorderRadius.circular(AppRadius.medium),
+        ),
+        child: FilledButton.icon(
+          style: FilledButton.styleFrom(
+            backgroundColor: Colors.transparent,
+            shadowColor: Colors.transparent,
+            minimumSize: const Size.fromHeight(48),
+          ),
+           onPressed: onPressed,
+          icon: Icon(icon),
+          label: Text(label),
+        ),
+      );
+    }
+
+    return OutlinedButton.icon(
+       onPressed: onPressed,
+      icon: Icon(icon),
+      label: Text(label),
+    );
+  }
+}

clients/flutter/lib/widgets/status_card.dart

@@ -0,0 +1,55 @@
+import 'package:flutter/material.dart';
+
+import '../theme/app_colors.dart';
+
+class StatusCard extends StatelessWidget {
+  const StatusCard({
+    required this.title,
+    required this.value,
+    required this.subtitle,
+    required this.icon,
+    required this.accentColor,
+    super.key,
+  });
+
+  final String title;
+  final String value;
+  final String subtitle;
+  final IconData icon;
+  final Color accentColor;
+
+  @override
+  Widget build(BuildContext context) {
+    return Card(
+      child: Padding(
+        padding: const EdgeInsets.all(AppSpacing.md),
+        child: Row(
+          children: [
+            Container(
+              width: 48,
+              height: 48,
+              decoration: BoxDecoration(
+                color: accentColor.withOpacity(0.16),
+                borderRadius: BorderRadius.circular(AppRadius.medium),
+              ),
+              child: Icon(icon, color: accentColor),
+            ),
+            const SizedBox(width: AppSpacing.md),
+            Expanded(
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  Text(title, style: Theme.of(context).textTheme.bodyMedium),
+                  const SizedBox(height: AppSpacing.xs),
+                  Text(value, style: Theme.of(context).textTheme.headlineSmall),
+                  const SizedBox(height: AppSpacing.xs),
+                  Text(subtitle, style: Theme.of(context).textTheme.bodySmall),
+                ],
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

clients/flutter/lib/widgets/wifi_list_tile.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+
+import '../models/wifi_network.dart';
+import '../theme/app_colors.dart';
+
+class WifiListTile extends StatelessWidget {
+  const WifiListTile({
+    required this.network,
+    required this.onTap,
+    super.key,
+  });
+
+  final WifiNetwork network;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    return Card(
+      child: ListTile(
+        onTap: onTap,
+        contentPadding: const EdgeInsets.symmetric(
+          horizontal: AppSpacing.md,
+          vertical: AppSpacing.xs,
+        ),
+        leading: Container(
+          width: 48,
+          height: 48,
+          decoration: BoxDecoration(
+            color: AppColors.info.withOpacity(0.14),
+            borderRadius: BorderRadius.circular(AppRadius.medium),
+          ),
+          child: const Icon(Icons.wifi_rounded, color: AppColors.info),
+        ),
+        title: Text(network.ssid),
+        subtitle: Text('${network.security} · ${network.signalLabel}'),
+        trailing: const Icon(Icons.chevron_right_rounded),
+      ),
+    );
+  }
+}