```

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/observability/constants.py

@@ -9,7 +9,6 @@ class ObservabilityKey(StrEnum):
     REDIS = "redis"
     EVENTS = "events"
     WORKFLOWS = "workflows"
-    WRITEBACKS = "writebacks"
 
 
 class ObservabilityStatus(StrEnum):
@@ -24,4 +23,3 @@ class ObservabilityMetricKey(StrEnum):
     PENDING = "pending"
     FAILED = "failed"
     RUNNING = "running"
-    DISABLED = "disabled"