Add GitHub Pages documentation site and stable latest-main release publishing

[Copilot]

Mirrors the pages/release setup from klibio/example.pde.rcp: a Jekyll docs site with a dynamic downloads page backed by a rolling latest-main GitHub Release.

Jekyll docs site (_doc/)

• _config.yml — Jekyll config with jekyll-github-metadata, jekyll-seo-tag, jekyll-sitemap
• _layouts/default.html — Responsive layout with sticky nav and auto/light/dark theme toggle (localStorage-persisted)
• index.md — Project landing page; injects source_revision SHA link at build time
• downloads.md — Dynamically fetches the latest-main release from the GitHub Releases API and renders a bundle download table; degrades gracefully to a manual release link on error
• Gemfile — github-pages gem for local development

GitHub Actions

.github/workflows/jekyll-gh-pages.yml (new)

Triggers on main push or after Continuous Integration succeeds. Injects source_revision: $GITHUB_SHA into _config.yml, builds with actions/jekyll-build-pages, deploys via actions/deploy-pages.

.github/workflows/ci.yml (modified)

• Bug fix: job output timestamp was referencing the non-existent step id build-release; corrected to steps.timestamp.outputs.timestamp, making artifact names consistent across upload/download steps.
• New publish-latest-main job: runs only on main push, requires build-release success, downloads the dist bundle, then atomically replaces the latest-main prerelease with all built JARs — providing the stable download URL the docs page links to.

publish-latest-main:
  if: github.ref == 'refs/heads/main' && github.event_name == 'push'
  permissions:
    contents: write
  steps:
    - uses: actions/checkout@...
    - uses: actions/download-artifact@...
    - run: |
        gh release delete latest-main --yes --cleanup-tag 2>/dev/null || true
        gh release create latest-main --prerelease --target "${GITHUB_SHA}" "${JARS[@]}"

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