feat: 为openai分组增加messages调度开关和默认映射模型

backend/internal/service/openai_gateway_messages.go

@@ -28,6 +28,7 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 	account *Account,
 	body []byte,
 	promptCacheKey string,
+	defaultMappedModel string,
 ) (*OpenAIForwardResult, error) {
 	startTime := time.Now()
 
@@ -47,6 +48,10 @@ func (s *OpenAIGatewayService) ForwardAsAnthropic(
 
 	// 3. Model mapping
 	mappedModel := account.GetMappedModel(originalModel)
+	// 分组级降级：账号未映射时使用分组默认映射模型
+	if mappedModel == originalModel && defaultMappedModel != "" {
+		mappedModel = defaultMappedModel
+	}
 	responsesReq.Model = mappedModel
 
 	logger.L().Debug("openai messages: model mapping applied",