feat: 出库/借库记录记录并展示库位快照（DB加列+后端写入+记录页展示）

inventory-backend/app/services/trans_service.py

@@ -152,6 +152,8 @@ class TransService:
                     borrow_signature=signature,
                     remark=remark,
                     expected_return_time=expected_return_time,
+                    # [新增] 记录借出时的库位快照
+                    location=getattr(stock, 'warehouse_location', None),
                     status='borrowed',
                     is_returned=False
                 )