fix(order): persist cleared courier tracking numbers

order/src/main/java/com/baiyue/order/entity/OrderEntity.java

@@ -64,6 +64,8 @@ public class OrderEntity extends BaseEntity {
     private Long rootOrderId;
     private Integer splitSequence;
     private String expressCompany;
+    // 客户清空单号或改用其他交货方式时，必须把 NULL 写入数据库。
+    @TableField(updateStrategy = FieldStrategy.ALWAYS)
     private String expressTrackingNo;
     private LocalDateTime submittedAt;
     private LocalDateTime completedAt;