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

controller/relay.go

@@ -151,7 +151,7 @@ func Relay(c *gin.Context, relayFormat types.RelayFormat) {
 
 	priceData, err := helper.ModelPriceHelper(c, relayInfo, tokens, meta)
 	if err != nil {
-		newAPIError = types.NewError(err, types.ErrorCodeModelPriceError)
+		newAPIError = types.NewError(err, types.ErrorCodeModelPriceError, types.ErrOptionWithStatusCode(http.StatusBadRequest))
 		return
 	}