Add Helm chart and health probe endpoint

[luispabon]

Summary

• add a lightweight GET /healthz endpoint and wire it into the Compose example
• add a production-usable Helm chart with optional ingress, HPA, and PDB resources plus configurable runtime and scheduling values
• add Helm lint/template tooling, chart publishing via GitHub Pages/chart-releaser, and Artifact Hub repository metadata

Verification

• make helm-lint
• make helm-template
• helm package charts/readability-js-server --destination /tmp/readability-js-server-chart-review
• docker run --rm -v /home/luis/Projects/readability-js-server:/workspace -w /workspace -e PNPM_CONFIG_MINIMUM_RELEASE_AGE=0 node:24-bullseye bash -lc 'corepack enable && pnpm install --frozen-lockfile && pnpm lint && pnpm test'

Review

• final review status: pass
• residual risk: chart behavior was validated by lint/render/package rather than a live cluster deploy, which matches the approved verification scope