```

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/tools/init_db.py

@@ -1,5 +1,4 @@
 from app.core.database import Base, engine
-from app.modules.approvals.models import ApprovalRequest
 from app.modules.audit.models import AuditLog
 from app.modules.business.models import (
     AttendanceRecord,
@@ -21,10 +20,8 @@ from app.modules.business.models import (
 from app.modules.feishu.models import FeishuEventReceipt
 from app.modules.events.models import DomainEvent
 from app.modules.workflows.models import WorkflowAction, WorkflowInstance
-from app.modules.writebacks.models import OfficialWritebackRun
 
 _MODELS = [
-    ApprovalRequest,
     AuditLog,
     FeishuEventReceipt,
     Project,
@@ -45,7 +42,6 @@ _MODELS = [
     DomainEvent,
     WorkflowInstance,
     WorkflowAction,
-    OfficialWritebackRun,
 ]