feat: 添加视觉设计语言系统并重构认证页面UI

- 新增 visual_design_language.md 设计规范文档
- 新增 auth 设计 tokens (authBackground, authCard, authInput, feedback 系列等)
- 重构登录/注册/验证码/重置密码页面为新设计系统
- 新增 AuthHeroHeader, AuthSurfaceCard, AuthSection, AuthField, PasswordField 组件
- 重构 AppBanner 和 Toast 支持多类型配置 (info/success/warning/error)
- 后端 AgentScope: 重整 schemas/prompts/tools 作用域, 新增协议文档
- 更新 AGENTS.md 集成视觉设计语言约束

apps/lib/features/messages/data/inbox_api.dart

@@ -26,7 +26,7 @@ class InboxMessageResponse {
   final InboxMessageType messageType;
   final String? scheduleItemId;
   final String? friendshipId;
-  final String? content;
+  final Map<String, dynamic>? content;
   final bool isRead;
   final InboxMessageStatus status;
   final DateTime createdAt;
@@ -52,7 +52,7 @@ class InboxMessageResponse {
       messageType: InboxMessageType.fromJson(json['message_type'] as String),
       scheduleItemId: json['schedule_item_id'] as String?,
       friendshipId: json['friendship_id'] as String?,
-      content: json['content'] as String?,
+      content: json['content'] as Map<String, dynamic>?,
       isRead: json['is_read'] as bool,
       status: InboxMessageStatus.fromJson(json['status'] as String),
       createdAt: DateTime.parse(json['created_at'] as String),