refactor(repo): 收敛 base_model 双轨，删除函数统一走 repo.batch_delete_r

- shared/base_repository.py 新增 batch_delete_r（返回 R，等价原 base_model 语义）
- 20 个模块删除函数从 Model.batch_delete_r 改为 x_repo.batch_delete_r
- shared/base_model.py 移除 classmethod（get_by_id/get_by_ids/get_all_active/exists/batch_delete_r），只留字段 + to_dict
- 清理 base_model 多余 imports
- 实测 dept 删除、批量删除及多模块读接口正常

Co-Authored-By: Claude <noreply@anthropic.com>

modules/region/service.py

@@ -130,7 +130,7 @@ def update_city(request, data: CityForm):
 # 删除城市
 
 def delete_city(city_id):
-    return City.batch_delete_r(city_id)
+    return city_repo.batch_delete_r(city_id)
 # 根据城市ID获取子级城市
 
 def get_child_list(city_code):