```

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/security.py

@@ -40,34 +40,6 @@ def require_api_key(
     return principal
 
 
-def require_approval_api_key(
-    x_approval_api_key: str | None = Header(
-        default=None,
-        alias=HttpHeader.X_APPROVAL_API_KEY,
-    ),
-) -> ApiPrincipal:
-    """Validate the approval API key and return the approval principal."""
-
-    settings = get_settings()
-    if not settings.approval_api_key and not _has_enabled_keys(settings.approval_api_keys):
-        raise HTTPException(
-            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
-            detail=SecurityErrorDetail.APPROVAL_API_KEY_REQUIRED,
-        )
-    principal = _match_service_key(
-        x_approval_api_key,
-        settings.approval_api_key,
-        settings.approval_api_actor,
-        settings.approval_api_keys,
-    )
-    if principal is None:
-        raise HTTPException(
-            status_code=status.HTTP_401_UNAUTHORIZED,
-            detail=SecurityErrorDetail.INVALID_APPROVAL_API_KEY,
-        )
-    return principal
-
-
 def require_audit_api_key(
     x_audit_api_key: str | None = Header(
         default=None,