fix: display backend error message directly without i18n translation

backend/internal/handler/admin/account_handler.go

@@ -1127,12 +1127,6 @@ func (h *AccountHandler) BulkUpdate(c *gin.Context) {
 			c.JSON(409, gin.H{
 				"error":   "mixed_channel_warning",
 				"message": mixedErr.Error(),
-				"details": gin.H{
-					"group_id":         mixedErr.GroupID,
-					"group_name":       mixedErr.GroupName,
-					"current_platform": mixedErr.CurrentPlatform,
-					"other_platform":   mixedErr.OtherPlatform,
-				},
 			})
 			return
 		}