feat: 支局长/领导可指定客户经理创建记录

后端 schema: WorkPlanCreate/MiniBusinessCreate/KeyVisitCreate 新增可选 manager_id
后端 API: create 端点支持 manager_id 参数(留空则默认本人)
前端: 三个页面新建弹窗新增「客户经理」下拉(仅支局长/领导可见)

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

backend/app/api/key_visits.py

@@ -63,7 +63,7 @@ async def create_key_visit(
         planned_date=data.planned_date,
         planned_visitor=data.planned_visitor,
         visit_target=data.visit_target,
-        manager_id=uuid.UUID(current_user["user_id"]),
+        manager_id=data.manager_id or uuid.UUID(current_user["user_id"]),
     )
     init_entry(k, current_user["name"])
     db.add(k)