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/models/outbound.py

@@ -133,6 +133,9 @@ class TransOutbound(db.Model):
     outbound_time = db.Column(db.DateTime, default=beijing_time)
     operator_name = db.Column(db.String(100))  # 操作员
 
+    # [新增] 出库时的库位快照（从源库存记录带出，便于历史追溯）
+    warehouse_location = db.Column(db.String(100))
+
     remark = db.Column(db.Text)
 
     def to_dict(self):
@@ -148,5 +151,6 @@ class TransOutbound(db.Model):
             'signature_path': self.signature_path,
             'outbound_time': self.outbound_time.strftime('%Y-%m-%d %H:%M:%S') if self.outbound_time else None,
             'operator_name': self.operator_name,
+            'warehouse_location': self.warehouse_location or '',
             'remark': self.remark
         }