fix: added merchant_id in models of shipment module

shipment/models.py

@@ -103,6 +103,13 @@ class Shipment(ModelBase):
         help_text='用于兼容外部遗留系统的订单号（可空）',
     )
 
+    merchant = models.ForeignKey(
+        basic_models.Merchant,
+        on_delete=models.PROTECT,
+        related_name='shipments',
+        verbose_name='所属商户',
+    )
+
     customer = models.ForeignKey(
         basic_models.Customer,
         on_delete=models.PROTECT,
@@ -167,6 +174,13 @@ class SalesItem(ModelBase):
         verbose_name='出货单',
         help_text='为空表示待分配'
     )
+
+    merchant = models.ForeignKey(
+        basic_models.Merchant,
+        on_delete=models.PROTECT,
+        related_name='sales_items',
+        verbose_name='所属商户',
+    )
     
     name = models.CharField(
         max_length=200,