Helm CI on GitHub Actions

Chart dependency updates and linting run cold every time.

Why it happens

The Helm repository cache is not persisted, so every repo index is fetched again.

What to change

1. Cache ~/.cache/helm keyed on Chart.lock
2. Run helm lint and helm template in one job to reuse the cache
3. Use chart-testing for a consistent lint and install cycle

Helm on runnerhut

jobs:
  lint:
    runs-on: runnerhut-2vcpu-ubuntu-2404
    steps:
      - uses: actions/checkout@v4
      - run: helm dependency update ./chart
      - run: helm lint ./chart && helm template ./chart

The only runnerhut-specific line is `runs-on: runnerhut-2vcpu-ubuntu-2404`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.