feat(app): 实现认证模块 — F2 Auth BLoC + 登录/注册/角色选择/班级码加入

新增文件 (10):
- data/models/user.dart — 用户+角色模型 (匹配后端 UserResp/RoleResp)
- data/models/auth_token.dart — 认证令牌模型 (匹配后端 LoginResp)
- data/repositories/auth_repository.dart — 认证仓库 (JWT 安全持久化 + PIPL 合规)
- features/auth/bloc/auth_bloc.dart — 认证 BLoC (8 种事件, 6 种状态)
- features/auth/bloc/auth_event.dart — 认证事件 (sealed class 穷尽匹配)
- features/auth/bloc/auth_state.dart — 认证状态 (Authenticated 含角色/班级码流程)
- features/auth/views/login_page.dart — 登录/注册页面 (重写占位页面)
- features/auth/views/role_selection_page.dart — 角色选择页 (4 种角色卡片)
- features/auth/views/class_code_join_page.dart — 班级码加入页 (6 位输入)

修改文件 (5):
- pubspec.yaml — 添加 flutter_secure_storage 依赖
- app.dart — 注入 AuthBloc + RepositoryProvider
- main.dart — 简化入口 (认证恢复在 BLoC 中处理)
- core/routing/app_router.dart — 添加认证路由守卫 + 2 新路由
- erp-diary/service/class_service.rs — 移除未使用的 PaginatorTrait import

验证: flutter analyze (0 error) + cargo check 通过

app/lib/features/auth/bloc/auth_bloc.dart

@@ -0,0 +1,180 @@
+// 认证 BLoC — 管理用户登录状态和认证流程
+//
+// 状态机: AuthInitial → AuthLoading → Unauthenticated/Authenticated
+//                                     ↕
+//                                  Authenticating → Authenticated/AuthError
+
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:logger/logger.dart';
+
+import '../../../data/models/auth_token.dart';
+import '../../../data/models/user.dart';
+import '../../../data/remote/api_client.dart';
+import '../../../data/repositories/auth_repository.dart';
+
+part 'auth_event.dart';
+part 'auth_state.dart';
+
+/// 认证 BLoC — 处理所有认证相关的状态转换
+class AuthBloc extends Bloc<AuthEvent, AuthState> {
+  final AuthRepository _authRepository;
+  final Logger _logger = Logger(printer: PrettyPrinter(methodCount: 0));
+
+  AuthBloc({required AuthRepository authRepository})
+      : _authRepository = authRepository,
+        super(const AuthInitial()) {
+    // 注册事件处理器
+    on<AppStarted>(_onAppStarted);
+    on<LoginRequested>(_onLoginRequested);
+    on<RegisterRequested>(_onRegisterRequested);
+    on<RoleSelected>(_onRoleSelected);
+    on<ClassCodeSubmitted>(_onClassCodeSubmitted);
+    on<LogoutRequested>(_onLogoutRequested);
+    on<TokenRefreshed>(_onTokenRefreshed);
+    on<AuthExpired>(_onAuthExpired);
+  }
+
+  /// App 启动 — 从本地存储恢复认证状态
+  Future<void> _onAppStarted(
+    AppStarted event,
+    Emitter<AuthState> emit,
+  ) async {
+    emit(const AuthLoading());
+    try {
+      final user = await _authRepository.restoreAuth();
+      if (user != null) {
+        emit(Authenticated(
+          user: user,
+          needsRoleSelection: !user.hasRole,
+        ));
+      } else {
+        emit(const Unauthenticated());
+      }
+    } catch (e) {
+      _logger.e('恢复认证状态失败: $e');
+      emit(const Unauthenticated());
+    }
+  }
+
+  /// 用户登录
+  Future<void> _onLoginRequested(
+    LoginRequested event,
+    Emitter<AuthState> emit,
+  ) async {
+    emit(const Authenticating());
+    try {
+      final user = await _authRepository.login(
+        username: event.username,
+        password: event.password,
+      );
+      emit(Authenticated(
+        user: user,
+        needsRoleSelection: !user.hasRole,
+      ));
+    } on AuthException catch (e) {
+      _logger.w('登录失败: ${e.message}');
+      emit(AuthError(e.message));
+    } on OfflineException {
+      emit(const AuthError('网络不可用，请检查网络连接', retryable: true));
+    } catch (e) {
+      _logger.e('登录异常: $e');
+      emit(const AuthError('登录失败，请稍后重试'));
+    }
+  }
+
+  /// 用户注册
+  Future<void> _onRegisterRequested(
+    RegisterRequested event,
+    Emitter<AuthState> emit,
+  ) async {
+    emit(const Authenticating(isRegister: true));
+    try {
+      final user = await _authRepository.register(
+        username: event.username,
+        password: event.password,
+        displayName: event.displayName,
+      );
+      // 注册成功后需要选择角色
+      emit(Authenticated(
+        user: user,
+        needsRoleSelection: true,
+      ));
+    } on AuthException catch (e) {
+      _logger.w('注册失败: ${e.message}');
+      emit(AuthError(e.message));
+    } on OfflineException {
+      emit(const AuthError('网络不可用，请检查网络连接', retryable: true));
+    } catch (e) {
+      _logger.e('注册异常: $e');
+      emit(const AuthError('注册失败，请稍后重试'));
+    }
+  }
+
+  /// 用户选择角色
+  Future<void> _onRoleSelected(
+    RoleSelected event,
+    Emitter<AuthState> emit,
+  ) async {
+    final currentState = state;
+    if (currentState is! Authenticated) return;
+
+    // 根据角色决定下一步
+    final needsClassCode =
+        event.role == UserRoleType.student || event.role == UserRoleType.parent;
+
+    emit(currentState.copyWith(
+      needsRoleSelection: false,
+      needsClassCode: needsClassCode,
+    ));
+
+    _logger.i('角色选择: ${event.role.name}, 需要班级码: $needsClassCode');
+  }
+
+  /// 班级码加入
+  Future<void> _onClassCodeSubmitted(
+    ClassCodeSubmitted event,
+    Emitter<AuthState> emit,
+  ) async {
+    final currentState = state;
+    if (currentState is! Authenticated) return;
+
+    // TODO: 调用后端 API 验证班级码并加入班级
+    // 当前先标记为已完成，班级码验证在 F8 阶段完善
+    emit(currentState.copyWith(
+      needsClassCode: false,
+    ));
+
+    _logger.i('班级码加入: ${event.classCode}');
+  }
+
+  /// 用户登出
+  Future<void> _onLogoutRequested(
+    LogoutRequested event,
+    Emitter<AuthState> emit,
+  ) async {
+    try {
+      await _authRepository.logout();
+    } catch (e) {
+      _logger.w('登出失败（忽略）: $e');
+    }
+    emit(const Unauthenticated());
+  }
+
+  /// 令牌刷新成功
+  Future<void> _onTokenRefreshed(
+    TokenRefreshed event,
+    Emitter<AuthState> emit,
+  ) async {
+    _logger.d('令牌已刷新');
+    // 不改变当前状态，仅更新令牌
+  }
+
+  /// 认证过期（401 拦截器触发）
+  Future<void> _onAuthExpired(
+    AuthExpired event,
+    Emitter<AuthState> emit,
+  ) async {
+    _logger.w('认证过期，需要重新登录');
+    emit(const Unauthenticated());
+  }
+}