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

types/error.go

@@ -390,6 +390,12 @@ func ErrOptionWithNoRecordErrorLog() NewAPIErrorOptions {
 	}
 }
 
+func ErrOptionWithStatusCode(statusCode int) NewAPIErrorOptions {
+	return func(e *NewAPIError) {
+		e.StatusCode = statusCode
+	}
+}
+
 func ErrOptionWithHideErrMsg(replaceStr string) NewAPIErrorOptions {
 	return func(e *NewAPIError) {
 		if common.DebugEnabled {