feat(auth): 添加登录/注册页面及令牌恢复流程

- 新增 SplashPage（启动页）和 LoginPage（登录页），支持路由跳转
- 扩展 AuthState，增加 submitting/alert/busy 状态及消费机制
- AuthController 增加 checkLoginState/register/showAlert 等方法
- 删除旧模型文件（binding_item, token_response, verify_response）
- 删除旧版 LoginPage，迁移至 features/auth 目录
- 更新本地化字符串，增加注册相关文案
- 调整默认 API 地址为本地开发环境

webrtc_controller_flutter/lib/l10n/app_localizations.dart

@@ -116,6 +116,30 @@ abstract class AppLocalizations {
   /// **'退出登录'**
   String get logout;
 
+  /// No description provided for @registerAccount.
+  ///
+  /// In zh, this message translates to:
+  /// **'注册新账号'**
+  String get registerAccount;
+
+  /// No description provided for @registerSuccess.
+  ///
+  /// In zh, this message translates to:
+  /// **'注册成功，请登录'**
+  String get registerSuccess;
+
+  /// No description provided for @registerFailed.
+  ///
+  /// In zh, this message translates to:
+  /// **'注册失败：{error}'**
+  String registerFailed(Object error);
+
+  /// No description provided for @loginSubtitle.
+  ///
+  /// In zh, this message translates to:
+  /// **'登录后可连接已绑定的被控设备'**
+  String get loginSubtitle;
+
   /// No description provided for @cancel.
   ///
   /// In zh, this message translates to: