feat(device): 启动自动连接 USB 串口 + 隐藏设置页配置项 + 标题栏连接状态

- 新增 AutoSerialConnect 服务：启动后自动连接第一个 USB 串口设备，
  固定 115200/8/N/1，连接失败时每 3s 重试，断开后重新进入重试循环
- main.dart 通过 ProviderContainer 在 runApp 之前触发 autoSerialConnectProvider
- 移除设置页「串口配置」菜单项及对应面板分支
- StatusBar 在「设备运行状态」前增加串口连接状态指示（已连接/连接中/未连接）

lib/features/settings/pages/settings_page.dart

@@ -5,11 +5,10 @@ import '../../../core/theme/app_theme.dart';
 import '../../../shared/widgets/common_button.dart';
 import '../widgets/language_panel.dart';
 import '../widgets/password_panel.dart';
-import '../widgets/serial_config_panel.dart';
 import '../widgets/usb_import_panel.dart';
 
 /// 设置页菜单
-enum _SettingsMenu { upgrade, language, password, usbImport, serialConfig }
+enum _SettingsMenu { upgrade, language, password, usbImport }
 
 /// 系统设置页面
 class SettingsPage extends ConsumerStatefulWidget {
@@ -70,14 +69,6 @@ class _SettingsPageState extends ConsumerState<SettingsPage> {
                       onTap: () => setState(
                           () => _currentMenu = _SettingsMenu.upgrade),
                     ),
-                    // 串口配置
-                    _buildMenuItem(
-                      icon: Icons.settings_input_hdmi,
-                      title: '串口配置',
-                      selected: _currentMenu == _SettingsMenu.serialConfig,
-                      onTap: () => setState(
-                          () => _currentMenu = _SettingsMenu.serialConfig),
-                    ),
                     // 语言设置
                     _buildMenuItem(
                       icon: Icons.language,
@@ -127,7 +118,6 @@ class _SettingsPageState extends ConsumerState<SettingsPage> {
 
   Widget _buildContent() {
     return switch (_currentMenu) {
-      _SettingsMenu.serialConfig => const SerialConfigPanel(),
       _SettingsMenu.language => const LanguagePanel(),
       _SettingsMenu.password => const PasswordPanel(),
       _SettingsMenu.usbImport => const UsbImportPanel(),