```

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。
```

alembic/env.py

@@ -5,13 +5,11 @@ from sqlalchemy import engine_from_config, pool
 
 from app.core.config import get_settings
 from app.core.db_base import Base
-from app.modules.approvals import models as approval_models
 from app.modules.audit import models as audit_models
 from app.modules.business import models as business_models
 from app.modules.events import models as event_models
 from app.modules.feishu import models as feishu_models
 from app.modules.workflows import models as workflow_models
-from app.modules.writebacks import models as writeback_models
 
 config = context.config
 
@@ -23,13 +21,11 @@ settings = get_settings()
 
 # Keep imports referenced so SQLAlchemy model classes register with Base.metadata.
 _REGISTERED_MODEL_MODULES = (
-    approval_models,
     audit_models,
     business_models,
     event_models,
     feishu_models,
     workflow_models,
-    writeback_models,
 )