fix: 亮灯表重复卡片 — 修复同客户经理同日多条拜访导致的 fan-out

- 原查询用 outerjoin(Visit, visit_date == MAX(visit_date)) 获取拜访方式,
  当同一天有多条拜访(协同拜访)时会扩展成多行,导致亮灯表同一客户显示多张卡片
- 改用 DISTINCT ON (manager_id, customer_id) 子查询,保证每对(经理,客户)
  只取最新一条拜访,消除重复
- 移除不再使用的 func 导入

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

backend/app/services/light_board.py

@@ -9,7 +9,7 @@ Status (rolling 30-day window):
 
 from datetime import date, timedelta
 from uuid import UUID
-from sqlalchemy import select, func, and_
+from sqlalchemy import select, and_
 from sqlalchemy.ext.asyncio import AsyncSession
 from app.models.user import User
 from app.models.customer import Customer
@@ -86,18 +86,28 @@ async def get_light_board(
     }
 
     # ── All customers with their last visit per manager ──
-    # Subquery: latest visit date + method per (manager_id, customer_id)
+    # Subquery: latest visit (date + method) per (manager_id, customer_id).
+    # DISTINCT ON keeps exactly one row per pair even when multiple visits
+    # share the same latest date (e.g. companion/collaborative visits),
+    # preventing fan-out that would duplicate customer cards on the board.
     latest_visit = (
         select(
             Visit.manager_id,
             Visit.customer_id,
-            func.max(Visit.visit_date).label("last_visit_date"),
+            Visit.visit_date.label("last_visit_date"),
+            Visit.visit_method.label("last_visit_method"),
+        )
+        .distinct(Visit.manager_id, Visit.customer_id)
+        .order_by(
+            Visit.manager_id,
+            Visit.customer_id,
+            Visit.visit_date.desc(),
+            Visit.id.desc(),
         )
-        .group_by(Visit.manager_id, Visit.customer_id)
         .subquery()
     )
 
-    # Join: assignments → customers → latest_visit → visits (for method)
+    # Join: assignments → customers → latest_visit (date + method)
     rows = await db.execute(
         select(
             CustomerAssignment.manager_id,
@@ -108,18 +118,13 @@ async def get_light_board(
             Customer.in_use_services,
             Customer.monthly_fee,
             latest_visit.c.last_visit_date,
-            Visit.visit_method,
+            latest_visit.c.last_visit_method,
         )
         .join(Customer, Customer.id == CustomerAssignment.customer_id)
         .outerjoin(latest_visit, and_(
             latest_visit.c.manager_id == CustomerAssignment.manager_id,
             latest_visit.c.customer_id == CustomerAssignment.customer_id,
         ))
-        .outerjoin(Visit, and_(
-            Visit.manager_id == CustomerAssignment.manager_id,
-            Visit.customer_id == CustomerAssignment.customer_id,
-            Visit.visit_date == latest_visit.c.last_visit_date,
-        ))
         .where(CustomerAssignment.role == "primary")
         .order_by(Customer.name)
     )