feat(工单): 添加工单缺陷数量字段并优化导入逻辑

为工单模型添加缺陷数量字段，优化Excel导入逻辑
增加必填字段校验和异常处理，完善默认值设置

DOAN.Model/MES/Product/ProWorkorder.cs

@@ -48,6 +48,12 @@ namespace DOAN.Model.MES.product
         [SugarColumn(ColumnName = "shipment_num")]
         public int? ShipmentNum { get; set; }
 
+        /// <summary>
+        /// 缺陷数量
+        /// </summary>
+        [SugarColumn(ColumnName = "defect_num")]
+        public int? DefectNum { get; set; }
+
         /// <summary>
         /// 序号 
         /// </summary>