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/mini_business.py

@@ -10,6 +10,7 @@ class MiniBusinessCreate(BaseModel):
     follow_up_detail: str = ""
     status: str = "跟进中"
     expected_revenue_date: str = ""
+    manager_id: Optional[uuid.UUID] = None
 
 
 class MiniBusinessUpdate(BaseModel):