Helm HTTP proxy fails with charts that have oci:// URLs

[NathanVaughn]

Thanks for the new release! I noticed that the Helm HTTP proxy will error out when the underlying chart has an oci:// url.
For example: https://stakater.github.io/stakater-charts/index.yaml

  konfigurator:
  - apiVersion: v1
    created: "2024-10-11T10:37:50.358372394Z"
    description: Konfigurator chart that runs on kubernetes
    digest: f289013c4aafe437c666cb179301ba1493d0f115f070dafd6216ee9ff5708803
    home: https://github.com/stakater/konfigurator
    icon: https://raw.githubusercontent.com/stakater/Konfigurator/master/assets/web/Konfigurator-round-100px.png
    keywords:
    - Konfigurator
    - kubernetes
    maintainers:
    - email: hello@stakater.com
      name: Stakater
    name: konfigurator
    urls:
    - oci://ghcr.io/stakater/saap-catalog/charts/konfigurator-0.1.40.tgz
    version: 0.1.40

This condition gets triggered

proxy/internal/handler/helm.go

Lines 290 to 293 in bb2205a

	downloadURL := baseURL.ResolveReference(reference)
	if (downloadURL.Scheme != "http" && downloadURL.Scheme != "https") || downloadURL.Host == "" {
	return helmChartRelease{}, fmt.Errorf("chart %q URL must be HTTP(S)", chartName)
	}

and this error is produced:

warn time=2026-09-04T21:43:09.575Z level=WARN msg="failed to rewrite Helm index" repository=stakater error="chart \"konfigurator\" URL must be HTTP(S)"

It would be nice if it could automatically rewrite the URL if an OCI proxy is also configured already too.