fix: record upstream error message in backend image log other data

Pass errMsg into other[error_message] so it persists to the database and can be queried by the frontend.

relay/image_handler.go

@@ -210,6 +210,7 @@ func logImageError(c *gin.Context, info *relaycommon.RelayInfo, request *dto.Ima
 		other["request_path"] = c.Request.URL.Path
 	}
 	other["is_image_error"] = true
+	other["error_message"] = errMsg
 
 	model.RecordConsumeLog(c, info.UserId, model.RecordConsumeLogParams{
 		ChannelId:    info.ChannelId,