feat: 账户关联根部门 + 员工新增自动带出账户

1. 账户管理：新建/编辑时可勾选关联 level=0 根部门（公司/分公司/子公司）
2. 后端新增 API：
   - PUT /social/accounts/:id/departments 批量关联根部门
   - GET /social/accounts/:id/departments 查询已关联部门
   - GET /social/department-account/:departmentId 按部门带出适用账户+标准
3. 部门更新 API 支持 socialAccountId/housingAccountId 字段
4. 员工新增表单：选定部门后自动带出社保公积金账户，可手动调整
5. 参保记录创建时写入 accountId

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

frontend/src/lib/api-services.ts

@@ -547,6 +547,15 @@ export const socialAccountApi = {
   /** 按员工获取适用账户 */
   employeeAccount: (employeeId: string) =>
     get(`/social/employee-account/${employeeId}`).then(unwrap<any>()),
+  /** 获取账户已关联的根部门 */
+  accountDepartments: (id: string) =>
+    get(`/social/accounts/${id}/departments`).then(unwrap<any[]>()),
+  /** 账户关联根部门（批量） */
+  linkDepartments: (id: string, departmentIds: string[]) =>
+    put(`/social/accounts/${id}/departments`, { departmentIds }).then(unwrap<any>()),
+  /** 按部门获取适用账户（选部门时自动带出） */
+  departmentAccount: (departmentId: string) =>
+    get(`/social/department-account/${departmentId}`).then(unwrap<any>()),
 }
 
 export const socialInsuranceApi = {