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/features/auth/domain/auth_state.dart

@@ -3,12 +3,22 @@ import 'package:freezed_annotation/freezed_annotation.dart';
 part 'auth_state.freezed.dart';
 
 /// 登录状态。
+///
+/// [alert] 为一次性提示（登录失效、注册成功等），UI 展示后须调用
+/// `AuthController.consumeAlert()` 消费，避免重建时重复弹出。
 @freezed
 class AuthState with _$AuthState {
+  const AuthState._();
+
   const factory AuthState({
     @Default(false) bool loggedIn,
     @Default(false) bool restoring,
+    @Default(false) bool submitting,
     String? username,
     String? error,
+    String? alert,
   }) = _AuthState;
+
+  /// 是否应禁用输入与提交按钮。
+  bool get busy => submitting || restoring;
 }

webrtc_controller_flutter/lib/features/auth/domain/auth_state.freezed.dart

@@ -19,8 +19,10 @@ final _privateConstructorUsedError = UnsupportedError(
 mixin _$AuthState {
   bool get loggedIn => throw _privateConstructorUsedError;
   bool get restoring => throw _privateConstructorUsedError;
+  bool get submitting => throw _privateConstructorUsedError;
   String? get username => throw _privateConstructorUsedError;
   String? get error => throw _privateConstructorUsedError;
+  String? get alert => throw _privateConstructorUsedError;
 
   /// Create a copy of AuthState
   /// with the given fields replaced by the non-null parameter values.
@@ -34,7 +36,14 @@ abstract class $AuthStateCopyWith<$Res> {
   factory $AuthStateCopyWith(AuthState value, $Res Function(AuthState) then) =
       _$AuthStateCopyWithImpl<$Res, AuthState>;
   @useResult
-  $Res call({bool loggedIn, bool restoring, String? username, String? error});
+  $Res call({
+    bool loggedIn,
+    bool restoring,
+    bool submitting,
+    String? username,
+    String? error,
+    String? alert,
+  });
 }
 
 /// @nodoc
@@ -54,8 +63,10 @@ class _$AuthStateCopyWithImpl<$Res, $Val extends AuthState>
   $Res call({
     Object? loggedIn = null,
     Object? restoring = null,
+    Object? submitting = null,
     Object? username = freezed,
     Object? error = freezed,
+    Object? alert = freezed,
   }) {
     return _then(
       _value.copyWith(
@@ -67,6 +78,10 @@ class _$AuthStateCopyWithImpl<$Res, $Val extends AuthState>
                 ? _value.restoring
                 : restoring // ignore: cast_nullable_to_non_nullable
                       as bool,
+            submitting: null == submitting
+                ? _value.submitting
+                : submitting // ignore: cast_nullable_to_non_nullable
+                      as bool,
             username: freezed == username
                 ? _value.username
                 : username // ignore: cast_nullable_to_non_nullable
@@ -75,6 +90,10 @@ class _$AuthStateCopyWithImpl<$Res, $Val extends AuthState>
                 ? _value.error
                 : error // ignore: cast_nullable_to_non_nullable
                       as String?,
+            alert: freezed == alert
+                ? _value.alert
+                : alert // ignore: cast_nullable_to_non_nullable
+                      as String?,
           )
           as $Val,
     );
@@ -90,7 +109,14 @@ abstract class _$$AuthStateImplCopyWith<$Res>
   ) = __$$AuthStateImplCopyWithImpl<$Res>;
   @override
   @useResult
-  $Res call({bool loggedIn, bool restoring, String? username, String? error});
+  $Res call({
+    bool loggedIn,
+    bool restoring,
+    bool submitting,
+    String? username,
+    String? error,
+    String? alert,
+  });
 }
 
 /// @nodoc
@@ -109,8 +135,10 @@ class __$$AuthStateImplCopyWithImpl<$Res>
   $Res call({
     Object? loggedIn = null,
     Object? restoring = null,
+    Object? submitting = null,
     Object? username = freezed,
     Object? error = freezed,
+    Object? alert = freezed,
   }) {
     return _then(
       _$AuthStateImpl(
@@ -122,6 +150,10 @@ class __$$AuthStateImplCopyWithImpl<$Res>
             ? _value.restoring
             : restoring // ignore: cast_nullable_to_non_nullable
                   as bool,
+        submitting: null == submitting
+            ? _value.submitting
+            : submitting // ignore: cast_nullable_to_non_nullable
+                  as bool,
         username: freezed == username
             ? _value.username
             : username // ignore: cast_nullable_to_non_nullable
@@ -130,6 +162,10 @@ class __$$AuthStateImplCopyWithImpl<$Res>
             ? _value.error
             : error // ignore: cast_nullable_to_non_nullable
                   as String?,
+        alert: freezed == alert
+            ? _value.alert
+            : alert // ignore: cast_nullable_to_non_nullable
+                  as String?,
       ),
     );
   }
@@ -137,13 +173,15 @@ class __$$AuthStateImplCopyWithImpl<$Res>
 
 /// @nodoc
 
-class _$AuthStateImpl implements _AuthState {
+class _$AuthStateImpl extends _AuthState {
   const _$AuthStateImpl({
     this.loggedIn = false,
     this.restoring = false,
+    this.submitting = false,
     this.username,
     this.error,
-  });
+    this.alert,
+  }) : super._();
 
   @override
   @JsonKey()
@@ -152,13 +190,18 @@ class _$AuthStateImpl implements _AuthState {
   @JsonKey()
   final bool restoring;
   @override
+  @JsonKey()
+  final bool submitting;
+  @override
   final String? username;
   @override
   final String? error;
+  @override
+  final String? alert;
 
   @override
   String toString() {
-    return 'AuthState(loggedIn: $loggedIn, restoring: $restoring, username: $username, error: $error)';
+    return 'AuthState(loggedIn: $loggedIn, restoring: $restoring, submitting: $submitting, username: $username, error: $error, alert: $alert)';
   }
 
   @override
@@ -170,14 +213,24 @@ class _$AuthStateImpl implements _AuthState {
                 other.loggedIn == loggedIn) &&
             (identical(other.restoring, restoring) ||
                 other.restoring == restoring) &&
+            (identical(other.submitting, submitting) ||
+                other.submitting == submitting) &&
             (identical(other.username, username) ||
                 other.username == username) &&
-            (identical(other.error, error) || other.error == error));
+            (identical(other.error, error) || other.error == error) &&
+            (identical(other.alert, alert) || other.alert == alert));
   }
 
   @override
-  int get hashCode =>
-      Object.hash(runtimeType, loggedIn, restoring, username, error);
+  int get hashCode => Object.hash(
+    runtimeType,
+    loggedIn,
+    restoring,
+    submitting,
+    username,
+    error,
+    alert,
+  );
 
   /// Create a copy of AuthState
   /// with the given fields replaced by the non-null parameter values.
@@ -188,22 +241,29 @@ class _$AuthStateImpl implements _AuthState {
       __$$AuthStateImplCopyWithImpl<_$AuthStateImpl>(this, _$identity);
 }
 
-abstract class _AuthState implements AuthState {
+abstract class _AuthState extends AuthState {
   const factory _AuthState({
     final bool loggedIn,
     final bool restoring,
+    final bool submitting,
     final String? username,
     final String? error,
+    final String? alert,
   }) = _$AuthStateImpl;
+  const _AuthState._() : super._();
 
   @override
   bool get loggedIn;
   @override
   bool get restoring;
   @override
+  bool get submitting;
+  @override
   String? get username;
   @override
   String? get error;
+  @override
+  String? get alert;
 
   /// Create a copy of AuthState
   /// with the given fields replaced by the non-null parameter values.