```

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/core/operation_guard.py

@@ -0,0 +1,16 @@
+from fastapi import HTTPException, status
+
+from app.core.config import get_settings
+
+
+READ_ONLY_OPERATION_DISABLED = "This service is read-only; data mutation operations are disabled"
+
+
+def require_operations_enabled(detail: str = READ_ONLY_OPERATION_DISABLED) -> None:
+    """Reject mutation-oriented endpoints when the product is running read-only."""
+
+    if get_settings().read_only_mode:
+        raise HTTPException(
+            status_code=status.HTTP_405_METHOD_NOT_ALLOWED,
+            detail=detail,
+        )