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

backend/src/v1/schedule_items/service.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import json
 from typing import TYPE_CHECKING, Protocol, Literal
 from uuid import UUID
 
@@ -345,26 +344,22 @@ class ScheduleItemService(BaseService):
                     )
                 elif existing_msg.status == InboxMessageStatus.REJECTED:
                     existing_msg.status = InboxMessageStatus.PENDING
-                    existing_msg.content = json.dumps(
-                        {
-                            "type": "invite",
-                            "permission": request_permission,
-                            "action": "pending",
-                        }
-                    )
+                    existing_msg.content = {
+                        "type": "invite",
+                        "permission": request_permission,
+                        "action": "pending",
+                    }
             else:
                 message = InboxMessage(
                     recipient_id=recipient_id,
                     sender_id=user_id,
                     message_type=InboxMessageType.CALENDAR,
                     schedule_item_id=item.id,
-                    content=json.dumps(
-                        {
-                            "type": "invite",
-                            "permission": request_permission,
-                            "action": "pending",
-                        }
-                    ),
+                    content={
+                        "type": "invite",
+                        "permission": request_permission,
+                        "action": "pending",
+                    },
                     created_by=user_id,
                 )
                 self._session.add(message)
@@ -432,7 +427,7 @@ class ScheduleItemService(BaseService):
                     status_code=404, detail="No pending invitation found"
                 )
 
-            content = json.loads(inbox.content or "{}")
+            content = inbox.content or {}
             permission = content.get("permission", 1)
 
             existing = await self._repository.get_subscription(item_id, user_id)
@@ -505,13 +500,11 @@ class ScheduleItemService(BaseService):
             if sub.subscriber_id == user_id:
                 continue
 
-            content = json.dumps(
-                {
-                    "type": action_type,
-                    "title": title,
-                    "action": action_type,
-                }
-            )
+            content = {
+                "type": action_type,
+                "title": title,
+                "action": action_type,
+            }
 
             message = InboxMessage(
                 recipient_id=sub.subscriber_id,