feat: 支局长/分管领导可为任意客户经理代填记录

后端:
- 5个模块的 Create/Update schema 新增可选 manager_id 字段
- POST 端点: director/leader 可指定 manager_id，manager 角色自动用自身
- PUT 端点: director/leader 可修改 manager_id，manager 角色禁止修改

前端（移动端+桌面端共10个页面）:
- 支局长/领导可见「客户经理」下拉选择框
- 创建和编辑时均可指定记录归属的客户经理
- 涵盖今日拜访、今日纪要、工作计划、商机跟单、要客拜访五个模块

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

backend/app/schemas/visit.py

@@ -16,6 +16,7 @@ class VisitCreate(BaseModel):
     companions: list[uuid.UUID] = []
     companion_names: list[str] = []
     photos: list[str] = []
+    manager_id: Optional[uuid.UUID] = None  # director/leader can specify
 
 
 class VisitUpdate(BaseModel):
@@ -28,6 +29,7 @@ class VisitUpdate(BaseModel):
     communication_content: Optional[str] = None
     customer_demand: Optional[str] = None
     companions: Optional[list[uuid.UUID]] = None
+    manager_id: Optional[uuid.UUID] = None
     companion_names: Optional[list[str]] = None
     photos: Optional[list[str]] = None