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/work_plan.py

@@ -9,6 +9,7 @@ class WorkPlanCreate(BaseModel):
     plan_content: str = ""
     plan_date: str  # "YYYY-MM-DD"
     status: str = "计划中"
+    manager_id: Optional[uuid.UUID] = None  # director can assign to a specific manager
 
 
 class WorkPlanUpdate(BaseModel):