```

refactor: 移除审批和回写功能模块

移除了整个审批(approvals)和官方回写(writebacks)功能模块，
包括相关模型、路由、服务和配置项。更新了数据库迁移文件，
删除了相关的审批请求表和官方回写运行表。同时从API路由器中
移除了相应的路由，并调整了安全常量和字段验证器以匹配变更。
```

app/api/router.py

@@ -2,7 +2,6 @@ from fastapi import APIRouter
 
 from app.core.constants import ApiResponseKey, ApiStatus
 from app.modules.ai_agent.routes import router as ai_router
-from app.modules.approvals.routes import router as approvals_router
 from app.modules.audit.routes import router as audit_router
 from app.modules.business.routes import router as business_router
 from app.modules.dashboard.routes import router as dashboard_router
@@ -13,7 +12,6 @@ from app.modules.observability.routes import router as observability_router
 from app.modules.reports.routes import router as reports_router
 from app.modules.risk.routes import router as risk_router
 from app.modules.workflows.routes import router as workflows_router
-from app.modules.writebacks.routes import router as writebacks_router
 
 api_router = APIRouter()
 
@@ -30,11 +28,9 @@ api_router.include_router(dashboard_router, prefix="/dashboard", tags=["dashboar
 api_router.include_router(legacy_mysql_router, prefix="/integrations/mysql", tags=["mysql"])
 api_router.include_router(feishu_router, prefix="/integrations/feishu", tags=["feishu"])
 api_router.include_router(ai_router, prefix="/ai", tags=["ai"])
-api_router.include_router(approvals_router, prefix="/approvals", tags=["approvals"])
 api_router.include_router(reports_router, prefix="/reports", tags=["reports"])
 api_router.include_router(risk_router, prefix="/risks", tags=["risks"])
 api_router.include_router(audit_router, prefix="/audit", tags=["audit"])
 api_router.include_router(events_router, prefix="/events", tags=["events"])
 api_router.include_router(workflows_router, prefix="/workflows", tags=["workflows"])
-api_router.include_router(writebacks_router, prefix="/writebacks", tags=["writebacks"])
 api_router.include_router(observability_router, tags=["observability"])