Add explicit Helm registry login for OCI chart publishing

[Copilot]

Helm chart should be published as an OCI package on every release, versioned from the git tag (ignoring Chart.yaml version).

The release workflow already had helm package --version + helm push to GHCR OCI, but relied on implicit credential sharing from docker/login-action. Added explicit helm registry login before push to ensure reliable OCI authentication in CI:

echo "${{ secrets.GITHUB_TOKEN }}" | helm registry login ghcr.io -u ${{ github.actor }} --password-stdin
helm package charts/drop --version "${VERSION#v}" --app-version "${VERSION#v}"
helm push drop-*.tgz oci://ghcr.io/${{ github.repository_owner }}/charts

Chart is published to oci://ghcr.io/breee/charts/drop:<version> on each release.

[Breee]

@copilot but there is no helm chart published yet I think? I did not find one in the packages

[Copilot]

@copilot but there is no helm chart published yet I think? I did not find one in the packages

The chart won't appear in packages until this PR is merged and the release workflow actually runs. The workflow triggers on:

1. Tag push (v*)
2. Weekly schedule (Mondays 06:00 UTC)
3. Manual dispatch (Actions tab → "Run workflow")

After merging, you can either push a new tag (git tag v0.x.x && git push origin v0.x.x) or trigger it manually from the Actions tab with force: true to publish the first chart to oci://ghcr.io/breee/charts/drop.