refactor(service): 将 AccountUsageService 的包级缓存改为依赖注入

backend/internal/service/antigravity_gateway_service.go

@@ -322,9 +322,6 @@ func (s *AntigravityGatewayService) Forward(ctx context.Context, c *gin.Context,
 
 	originalModel := claudeReq.Model
 	mappedModel := s.getMappedModel(account, claudeReq.Model)
-	if mappedModel != claudeReq.Model {
-		log.Printf("Antigravity model mapping: %s -> %s (account: %s)", claudeReq.Model, mappedModel, account.Name)
-	}
 
 	// 获取 access_token
 	if s.tokenProvider == nil {