```

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/constants.py

@@ -4,7 +4,6 @@ from enum import StrEnum
 class ActorValue(StrEnum):
     API = "api"
     AUDITOR = "auditor"
-    APPROVER = "approver"
     SYSTEM = "system"
     SCHEDULER = "scheduler"
     FEISHU = "feishu"
@@ -14,7 +13,6 @@ class HttpHeader(StrEnum):
     AUTHORIZATION = "Authorization"
     X_API_KEY = "X-API-Key"
     X_AUDIT_API_KEY = "X-Audit-API-Key"
-    X_APPROVAL_API_KEY = "X-Approval-API-Key"
     X_REQUEST_ID = "X-Request-ID"
 
 
@@ -29,8 +27,6 @@ class ApiStatus(StrEnum):
 class SecurityErrorDetail(StrEnum):
     API_KEY_REQUIRED = "API_KEY is required"
     INVALID_API_KEY = "Invalid API key"
-    APPROVAL_API_KEY_REQUIRED = "APPROVAL_API_KEY is required"
-    INVALID_APPROVAL_API_KEY = "Invalid approval API key"
     AUDIT_API_KEY_REQUIRED = "AUDIT_API_KEY is required"
     INVALID_AUDIT_API_KEY = "Invalid audit API key"