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/ui/screens/message_invite_list_screen.dart

@@ -1,5 +1,3 @@
-import 'dart:convert';
-
 import 'package:flutter/material.dart' hide BackButton;
 import 'package:go_router/go_router.dart';
 
@@ -139,13 +137,8 @@ class _MessageInviteListScreenState extends State<MessageInviteListScreen> {
     }
   }
 
-  Map<String, dynamic>? _parseCalendarContent(String? content) {
-    if (content == null) return null;
-    try {
-      return jsonDecode(content) as Map<String, dynamic>;
-    } catch (_) {
-      return null;
-    }
+  Map<String, dynamic>? _parseCalendarContent(Map<String, dynamic>? content) {
+    return content;
   }
 
   Future<(String calendarTitle, String senderName)?> _getCalendarInviteInfo(
@@ -250,7 +243,7 @@ class _MessageInviteListScreenState extends State<MessageInviteListScreen> {
     if (friendRequest == null) return;
 
     final title = '${friendRequest.sender.username} 请求添加您为好友';
-    final description = message.content;
+    final description = message.content?['message'] as String?;
     final statusText = isReadOnly
         ? (friendRequest.status == 'accepted'
               ? '已接受'
@@ -579,13 +572,8 @@ class _MessageCard extends StatelessWidget {
       return '${friendRequest!.sender.username} 请求添加您为好友';
     }
     if (message.messageType == InboxMessageType.calendar) {
-      try {
-        final data =
-            jsonDecode(message.content ?? '{}') as Map<String, dynamic>;
-        return data['title'] as String? ?? '日历邀请';
-      } catch (_) {
-        return '日历邀请';
-      }
+      final data = message.content;
+      return data?['title'] as String? ?? '日历邀请';
     }
     return '系统消息';
   }
@@ -594,11 +582,7 @@ class _MessageCard extends StatelessWidget {
     if (message.messageType == InboxMessageType.calendar) {
       Map<String, dynamic>? data;
       if (message.content != null) {
-        try {
-          data = jsonDecode(message.content!) as Map<String, dynamic>;
-        } catch (_) {
-          data = null;
-        }
+        data = message.content;
       }
       if (data == null) return '点击查看详情';
 
@@ -617,6 +601,6 @@ class _MessageCard extends StatelessWidget {
       }
       return '点击查看详情';
     }
-    return message.content ?? '点击查看详情';
+    return message.content?['message'] as String? ?? '点击查看详情';
   }
 }

apps/lib/features/messages/ui/widgets/calendar_message_card.dart

@@ -1,5 +1,3 @@
-import 'dart:convert';
-
 import 'package:flutter/material.dart';
 
 import '../../../../core/theme/design_tokens.dart';
@@ -19,13 +17,8 @@ class CalendarInviteCard extends StatelessWidget {
   });
 
   String? get eventTitle {
-    if (message.content == null) return null;
-    try {
-      final data = jsonDecode(message.content!) as Map<String, dynamic>;
-      return data['title'] as String?;
-    } catch (_) {
-      return null;
-    }
+    final data = message.content;
+    return data?['title'] as String?;
   }
 
   @override
@@ -101,13 +94,8 @@ class CalendarUpdateCard extends StatelessWidget {
   const CalendarUpdateCard({super.key, required this.message, this.onTap});
 
   String? get eventTitle {
-    if (message.content == null) return null;
-    try {
-      final data = jsonDecode(message.content!) as Map<String, dynamic>;
-      return data['title'] as String?;
-    } catch (_) {
-      return null;
-    }
+    final data = message.content;
+    return data?['title'] as String?;
   }
 
   @override
@@ -190,13 +178,8 @@ class CalendarDeleteCard extends StatelessWidget {
   const CalendarDeleteCard({super.key, required this.message});
 
   String? get eventTitle {
-    if (message.content == null) return null;
-    try {
-      final data = jsonDecode(message.content!) as Map<String, dynamic>;
-      return data['title'] as String?;
-    } catch (_) {
-      return null;
-    }
+    final data = message.content;
+    return data?['title'] as String?;
   }
 
   @override