feat: add OpenAI image generation controls

backend/internal/service/gateway_service.go

@@ -8367,6 +8367,7 @@ func (s *GatewayService) recordUsageCore(ctx context.Context, input *recordUsage
 		groupDefault := apiKey.Group.RateMultiplier
 		multiplier = s.getUserGroupRateMultiplier(ctx, user.ID, *apiKey.GroupID, groupDefault)
 	}
+	imageMultiplier := resolveImageRateMultiplier(apiKey, multiplier)
 
 	// 确定计费模型
 	billingModel := forwardResultBillingModel(result.Model, result.UpstreamModel)
@@ -8384,7 +8385,7 @@ func (s *GatewayService) recordUsageCore(ctx context.Context, input *recordUsage
 	}
 
 	// 计算费用
-	cost := s.calculateRecordUsageCost(ctx, result, apiKey, billingModel, multiplier, opts)
+	cost := s.calculateRecordUsageCost(ctx, result, apiKey, billingModel, multiplier, imageMultiplier, opts)
 
 	// 判断计费方式：订阅模式 vs 余额模式
 	isSubscriptionBilling := subscription != nil && apiKey.Group != nil && apiKey.Group.IsSubscriptionType()
@@ -8396,7 +8397,7 @@ func (s *GatewayService) recordUsageCore(ctx context.Context, input *recordUsage
 	// 创建使用日志
 	accountRateMultiplier := account.BillingRateMultiplier()
 	usageLog := s.buildRecordUsageLog(ctx, input, result, apiKey, user, account, subscription,
-		requestedModel, multiplier, accountRateMultiplier, billingType, cacheTTLOverridden, cost, opts)
+		requestedModel, multiplier, imageMultiplier, accountRateMultiplier, billingType, cacheTTLOverridden, cost, opts)
 
 	// 计算账号统计定价费用（使用最终上游模型匹配自定义规则）
 	if apiKey.GroupID != nil {
@@ -8450,11 +8451,12 @@ func (s *GatewayService) calculateRecordUsageCost(
 	apiKey *APIKey,
 	billingModel string,
 	multiplier float64,
+	imageMultiplier float64,
 	opts *recordUsageOpts,
 ) *CostBreakdown {
 	// 图片生成计费
 	if result.ImageCount > 0 {
-		return s.calculateImageCost(ctx, result, apiKey, billingModel, multiplier)
+		return s.calculateImageCost(ctx, result, apiKey, billingModel, imageMultiplier)
 	}
 
 	// Token 计费
@@ -8495,7 +8497,8 @@ func (s *GatewayService) calculateImageCost(
 			Model:          billingModel,
 			GroupID:        &gid,
 			Tokens:         tokens,
-			RequestCount:   1,
+			RequestCount:   result.ImageCount,
+			SizeTier:       result.ImageSize,
 			RateMultiplier: multiplier,
 			Resolver:       s.resolver,
 			Resolved:       resolved,
@@ -8580,6 +8583,7 @@ func (s *GatewayService) buildRecordUsageLog(
 	subscription *UserSubscription,
 	requestedModel string,
 	multiplier float64,
+	imageMultiplier float64,
 	accountRateMultiplier float64,
 	billingType int8,
 	cacheTTLOverridden bool,
@@ -8624,6 +8628,9 @@ func (s *GatewayService) buildRecordUsageLog(
 		SubscriptionID:        optionalSubscriptionID(subscription),
 		CreatedAt:             time.Now(),
 	}
+	if result.ImageCount > 0 {
+		usageLog.RateMultiplier = imageMultiplier
+	}
 	if cost != nil {
 		usageLog.InputCost = cost.InputCost
 		usageLog.OutputCost = cost.OutputCost