Replace implicit branch-based Pages publishing with an explicit deploy workflow

[Copilot]

The failing deploy job was coming from the repository’s Pages publishing path rather than dataset code changes. This updates the repo to build and deploy the site explicitly from the repository, instead of relying on the existing gh-pages branch flow.

• Move Pages publishing into Actions

  • Add .github/workflows/deploy.yml to build the Jekyll site and deploy it with actions/deploy-pages
  • Trigger on site/workflow changes and deploy from main

• Check in the actual site source

  • Bring the Jekyll site content into the repository root:
    • 404.html
    • _config.yml
    • _layouts/
    • _posts/
    • about.md
    • index.html
    • Gemfile / Gemfile.lock

• Remove layout/theme mismatches from the site

  • Switch pages using missing layouts (home, page) to the existing default layout
  • Simplify the Gemfile to the GitHub Pages dependency set
  • Replace runtime site.github.* dependencies in the layout with explicit repository metadata in _config.yml

• Keep generated artifacts out of Git

  • Update .gitignore for local Jekyll outputs and bundled gems

Example of the layout/config simplification:

# _config.yml
repository_url: "https://github.com/ME-ICA/open-multi-echo-data"
repository_nwo: "ME-ICA/open-multi-echo-data"
owner_name: "ME-ICA"
owner_url: "https://github.com/ME-ICA"

<!-- _layouts/default.html -->
<p class="view"><a href="{{ site.repository_url }}">View the Project on GitHub <small>{{ site.repository_nwo }}</small></a></p>