```

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/modules/legacy_mysql/routes.py

@@ -3,6 +3,7 @@ from sqlalchemy.orm import Session
 
 from app.core.database import get_db
 from app.core.masking import mask_configured
+from app.core.operation_guard import require_operations_enabled
 from app.core.security import ApiPrincipal, require_api_key
 from app.core.task_queue import enqueue_legacy_project_sync, enqueue_legacy_task_sync
 from app.modules.legacy_mysql.schemas import (
@@ -60,6 +61,7 @@ def sync_projects(
     db: Session = Depends(get_db),
     principal: ApiPrincipal = Depends(require_api_key),
 ) -> dict:
+    require_operations_enabled()
     result = LegacyMySQLService(db).sync_projects(
         source_query=payload.source_query,
         source_query_name=payload.source_query_name,
@@ -76,6 +78,7 @@ def enqueue_sync_projects(
     payload: LegacyProjectSyncRequest,
     principal: ApiPrincipal = Depends(require_api_key),
 ) -> dict:
+    require_operations_enabled()
     return enqueue_legacy_project_sync(
         source_query=payload.source_query,
         source_query_name=payload.source_query_name,
@@ -92,6 +95,7 @@ def sync_tasks(
     db: Session = Depends(get_db),
     principal: ApiPrincipal = Depends(require_api_key),
 ) -> dict:
+    require_operations_enabled()
     result = LegacyMySQLService(db).sync_tasks(
         source_query=payload.source_query,
         source_query_name=payload.source_query_name,
@@ -108,6 +112,7 @@ def enqueue_sync_tasks(
     payload: LegacyTaskSyncRequest,
     principal: ApiPrincipal = Depends(require_api_key),
 ) -> dict:
+    require_operations_enabled()
     return enqueue_legacy_task_sync(
         source_query=payload.source_query,
         source_query_name=payload.source_query_name,