fix(app): 家长同意验证流程 — PIPL 第28条合规

- 新增 ParentalConsentPage: 显示隐私政策要点 + 双重确认复选框
- 角色选择流程: 学生 → 家长同意确认 → 班级码输入
- Authenticated 状态: 添加 needsParentalConsent/parentalConsentAt/selectedRole
- ParentalConsentAccepted 事件: 记录同意时间戳
- 路由守卫: 注册 /parental-consent 路径和重定向逻辑
- 非学生角色（老师/家长/独立用户）不需要经过同意流程

审计 ID: S-03

app/lib/core/routing/app_router.dart

@@ -28,6 +28,7 @@ import '../../features/profile/views/profile_page.dart';
 import '../../features/editor/views/editor_page.dart';
 import '../../features/auth/views/login_page.dart';
 import '../../features/auth/views/role_selection_page.dart';
+import '../../features/auth/views/parental_consent_page.dart';
 import '../../features/auth/views/class_code_join_page.dart';
 import '../../features/onboarding/views/splash_page.dart';
 import '../../features/onboarding/views/onboarding_page.dart';
@@ -49,7 +50,7 @@ final _rootNavigatorKey = GlobalKey<NavigatorState>();
 final _shellNavigatorKey = GlobalKey<NavigatorState>();
 
 /// 不需要认证的白名单路径
-const _publicPaths = ['/splash', '/onboarding', '/login', '/role-selection', '/class-code'];
+const _publicPaths = ['/splash', '/onboarding', '/login', '/role-selection', '/parental-consent', '/class-code'];
 
 /// 创建路由配置 — 需要注入 AuthBloc
 GoRouter createAppRouter(AuthBloc authBloc) {
@@ -74,6 +75,7 @@ GoRouter createAppRouter(AuthBloc authBloc) {
       // 已认证 + 访问公开页面 → 根据状态重定向
       if (isAuthenticated && isPublicPath) {
         if (authState.needsRoleSelection) return '/role-selection';
+        if (authState.needsParentalConsent) return '/parental-consent';
         if (authState.needsClassCode) return '/class-code';
         return '/home';
       }
@@ -83,9 +85,14 @@ GoRouter createAppRouter(AuthBloc authBloc) {
         if (authState.needsRoleSelection && currentPath != '/role-selection') {
           return '/role-selection';
         }
+        if (authState.needsParentalConsent &&
+            currentPath != '/parental-consent') {
+          return '/parental-consent';
+        }
         if (authState.needsClassCode &&
             currentPath != '/class-code' &&
-            currentPath != '/role-selection') {
+            currentPath != '/role-selection' &&
+            currentPath != '/parental-consent') {
           return '/class-code';
         }
         return null;
@@ -125,6 +132,11 @@ GoRouter createAppRouter(AuthBloc authBloc) {
         name: 'roleSelection',
         builder: (context, state) => const RoleSelectionPage(),
       ),
+      GoRoute(
+        path: '/parental-consent',
+        name: 'parentalConsent',
+        builder: (context, state) => const ParentalConsentPage(),
+      ),
       GoRoute(
         path: '/class-code',
         name: 'classCode',