refactor: 移除多租户相关代码，重构为单租户架构

此次提交进行了大规模的架构重构：
1.  移除所有平台租户相关模块和代码，包括租户管理、套餐、订单、发票等功能
2.  将菜单模块从platform迁移到system模块，统一系统功能入口
3.  移除租户隔离相关的模型混入、中间件和配置
4.  简化文件上传、SSE事件总线、定时任务等模块的租户逻辑
5.  重构所有业务schema和模型，移除租户相关字段和关联
6.  清理初始化脚本、模板和常量中的租户相关代码
7.  简化认证和权限控制逻辑，移除数据范围检查相关代码

backend/app/api/v1/module_ai/chat/crud.py

@@ -23,7 +23,7 @@ class ChatSessionCRUD:
         """初始化CRUD数据层"""
         self.auth = auth
         self.user_id = auth.user.username or "user"
-        self.team_id = str(auth.user.tenant_id) if auth.user.tenant_id else None
+        self.team_id = "default"
         self.db = self._get_db()
 
     def _get_db(self) -> Any:

backend/app/api/v1/module_ai/chat/schema.py

@@ -2,7 +2,7 @@ from typing import Any
 
 from pydantic import BaseModel, ConfigDict, Field, field_validator
 
-from app.core.base_schema import BaseQueryParam, TenantByQueryParam, UserByQueryParam
+from app.core.base_schema import BaseQueryParam, UserByQueryParam
 
 
 class ChatQuerySchema(BaseModel):
@@ -53,7 +53,7 @@ class ChatSessionMessageSchema(BaseModel):
     model_config = ConfigDict(from_attributes=True)
 
 
-class ChatSessionQueryParam(BaseQueryParam, UserByQueryParam, TenantByQueryParam):
+class ChatSessionQueryParam(BaseQueryParam, UserByQueryParam):
     """会话查询参数"""
 
     title: str | None = Field(None, description="会话标题")

backend/app/api/v1/module_ai/chat/service.py

@@ -10,7 +10,6 @@ from agno.team.team import Team
 from redis.asyncio import Redis
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.api.v1.module_platform.tenant.service import TenantService
 from app.common.enums import RedisInitKeyConfig
 from app.common.request import PaginationService
 from app.core.base_schema import AuthSchema, PageResultSchema
@@ -73,9 +72,7 @@ async def _format_session_data(session: TeamSession, auth: AuthSchema | None = N
         try:
             team_id_str = session_dict.get("team_id")
             if team_id_str:
-                team_id = int(team_id_str)
-                tenant = await TenantService(auth, db).detail(id=team_id)
-            result["team_name"] = tenant.name
+                result["team_name"] = None
         except Exception:
             result["team_name"] = None
     else:
@@ -155,7 +152,7 @@ class ChatService:
                 session_id = session.session_id
 
             agno_factory = AgnoFactory()
-            team_id = str(self.auth.user.tenant_id or "default")
+            team_id = "default"
             agent = agno_factory.create_agent(
                 user_id=self.auth.user.username or "user",
                 team_id=team_id,
@@ -216,7 +213,7 @@ class ChatService:
                 session_id = session.session_id
 
             agno_factory = AgnoFactory()
-            team_id = str(self.auth.user.tenant_id or "default")
+            team_id = "default"
             agent: Team = agno_factory.create_agent(
                 user_id=self.auth.user.username or "user",
                 team_id=team_id,