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/schemas/key_visit.py

@@ -11,6 +11,7 @@ class KeyVisitCreate(BaseModel):
     planned_date: str = ""
     planned_visitor: str = ""
     visit_target: str = ""
+    manager_id: Optional[uuid.UUID] = None
 
 
 class KeyVisitUpdate(BaseModel):