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>

backend/src/routes/department.routes.ts

@@ -16,7 +16,10 @@ const createDeptSchema = z.object({
   description: z.string().max(200).optional(),
 })
 
-const updateDeptSchema = createDeptSchema.partial()
+const updateDeptSchema = createDeptSchema.partial().extend({
+  socialAccountId: z.string().nullable().optional(),
+  housingAccountId: z.string().nullable().optional(),
+})
 
 /** 获取部门树 */
 router.get('/', authMiddleware, async (req: AuthRequest, res, next) => {
@@ -109,6 +112,8 @@ router.put('/:id', authMiddleware, async (req: AuthRequest, res, next) => {
         ...(data.sortOrder !== undefined ? { sortOrder: data.sortOrder } : {}),
         ...(data.description !== undefined ? { description: data.description } : {}),
         ...(level !== undefined ? { level } : {}),
+        ...(data.socialAccountId !== undefined ? { socialAccountId: data.socialAccountId } : {}),
+        ...(data.housingAccountId !== undefined ? { housingAccountId: data.housingAccountId } : {}),
       },
     })
     res.json({ success: true, data: dept })