fix: 修复函数签名变更后的调用参数不匹配

- handleUpstreamError 补齐新增的三个参数 (0, "", false)
- handleStreamingResponse 移除已删除的 nil 参数

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/service/antigravity_gateway_service.go

@@ -1650,7 +1650,7 @@ func (s *AntigravityGatewayService) ForwardUpstream(ctx context.Context, c *gin.
 
 		// 429 错误时标记账号限流
 		if resp.StatusCode == http.StatusTooManyRequests {
-			s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, AntigravityQuotaScopeClaude)
+			s.handleUpstreamError(ctx, prefix, account, resp.StatusCode, resp.Header, respBody, AntigravityQuotaScopeClaude, 0, "", false)
 		}
 
 		// 透传上游错误

backend/internal/service/gateway_service_streaming_test.go

@@ -42,7 +42,7 @@ func TestGatewayService_StreamingReusesScannerBufferAndStillParsesUsage(t *testi
 		_, _ = pw.Write([]byte("data: [DONE]\n\n"))
 	}()
 
-	result, err := svc.handleStreamingResponse(context.Background(), resp, c, &Account{ID: 1}, time.Now(), "model", "model", nil, false)
+	result, err := svc.handleStreamingResponse(context.Background(), resp, c, &Account{ID: 1}, time.Now(), "model", "model", false)
 	_ = pr.Close()
 	require.NoError(t, err)
 	require.NotNil(t, result)