设备管理模块方法转换为DTO模式，修复long类型接收雪花ID丢失精度的问题

Model/Entity/Asset/EquipmentAttachmentEntity.cs

@@ -15,7 +15,7 @@ namespace Model.Entity.Asset
         /// <summary>
         /// 文件名称
         /// </summary>
-        [SugarColumn(Length = 200)]
+        [SugarColumn(Length = 200, IsNullable = true)]
         public string? FileName { get; set; }
 
         /// <summary>
@@ -26,13 +26,13 @@ namespace Model.Entity.Asset
         /// <summary>
         /// 文件扩展名（如 .pdf、.jpg）
         /// </summary>
-        [SugarColumn(Length = 20)]
+        [SugarColumn(Length = 20, IsNullable = true)]
         public string? FileExt { get; set; }
 
         /// <summary>
         /// 文件存储地址（上传后存储的相对路径）
         /// </summary>
-        [SugarColumn(Length = 200)]
+        [SugarColumn(Length = 200, IsNullable = true)]
         public string? FileUrl { get; set; }
 
         /// <summary>
@@ -43,13 +43,13 @@ namespace Model.Entity.Asset
         /// <summary>
         /// 上传人
         /// </summary>
-        [SugarColumn(Length = 50)]
+        [SugarColumn(Length = 50, IsNullable = true)]
         public string? Uploader { get; set; }
 
         /// <summary>
         /// 备注
         /// </summary>
-        [SugarColumn(Length = 500)]
+        [SugarColumn(Length = 500, IsNullable = true)]
         public string? Remark { get; set; }
     }
 }