feat(backend): 新增 /dashboard/user-operations 人员操作统计接口

- add_task_record 补 action_type=record 日志，使上传备注可统计到人
- get_user_operations 按人聚合 接收(receive)/转交(complete)/上传备注(record) 次数，时间筛选，中文名映射
- 复用 get_display_names，不新增数据库字段

backend/app/api/v1/endpoints/dashboard.py

@@ -10,6 +10,7 @@ from app.services.dashboard_service import (
     get_wip_tasks, WipTask,
     get_completed_tasks, CompletedTask,
     get_rejected_tasks, RejectedTask,
+    get_user_operations, UserOperation,
     get_people_workload, PersonWorkload,
     get_people_history, PersonHistoryRecord,
     search_product_messages, ProductMessageList,
@@ -70,6 +71,18 @@ async def rejected_tasks(
     return await get_rejected_tasks(db, since=since_dt, until=until_dt, limit=limit)
 
 
+@router.get("/user-operations", response_model=list[UserOperation])
+async def user_operations(
+    since: str | None = Query(None, description="起始日期 ISO 如 2026-08-01T00:00:00"),
+    until: str | None = Query(None, description="截止日期 ISO"),
+    db: AsyncSession = Depends(get_db),
+):
+    """人员操作统计 — 按人聚合 接收/转交/上传备注 次数，按时段过滤"""
+    since_dt = datetime.fromisoformat(since) if since else None
+    until_dt = datetime.fromisoformat(until) if until else None
+    return await get_user_operations(db, since=since_dt, until=until_dt)
+
+
 @router.get("/people-workload", response_model=list[PersonWorkload])
 async def people_workload(
     db: AsyncSession = Depends(get_db),