feat: improve model price error UX with role-aware messages and cleaner UI

- Backend: differentiate error messages for admin vs regular users in price.go
- Backend: include error_code in channel test response for structured error handling
- Frontend: render model_price_error as a styled card in Playground with admin nav button
- Frontend: show inline error details and settings link in channel test modal
- Frontend: parse error codes from both SSE and non-streaming API responses
- i18n: remove redundant "Settings" suffix from setting tab translations (en/fr/ru/ja/vi)
- i18n: update "Group & Model Pricing" translations across all locales

relay/responses_handler.go

@@ -143,7 +143,7 @@ func ResponsesHelper(c *gin.Context, info *relaycommon.RelayInfo) (newAPIError *
 		if err != nil {
 			info.OriginModelName = originModelName
 			info.PriceData = originPriceData
-			return types.NewError(err, types.ErrorCodeModelPriceError, types.ErrOptionWithSkipRetry())
+			return types.NewError(err, types.ErrorCodeModelPriceError, types.ErrOptionWithSkipRetry(), types.ErrOptionWithStatusCode(http.StatusBadRequest))
 		}
 		service.PostTextConsumeQuota(c, info, usageDto, nil)