Migrate from github-pages gem to GitHub Actions workflow

[Copilot]

The github-pages gem conflicts with individually specified Jekyll plugins in the Gemfile, causing dependency resolution failures.

Changes:

• Added .github/workflows/jekyll.yml: Standard Jekyll build/deploy workflow using actions/configure-pages and actions/deploy-pages
• Updated Gemfile:
  • Removed github-pages gem (source of version conflicts)
  • Removed connection_pool workaround
  • Specified Jekyll 4.3 directly
  • Added missing jekyll-gist and jekyll-paginate plugins referenced in _config.yml
  • Moved jekyll and webrick out of jekyll_plugins group

Before:

group :jekyll_plugins do
  gem 'jekyll'
  gem 'jekyll-feed'
  # ...
end
gem 'github-pages'  # Bundles its own Jekyll + plugin versions → conflict

After:

gem 'jekyll', '~> 4.3'
group :jekyll_plugins do
  gem 'jekyll-feed'
  # ...
end

The workflow uses Ruby 3.3 and enables bundler caching for faster builds.

Original prompt

Annotations
1 warning
build
The github-pages gem can't satisfy your Gemfile's dependencies. If you want to use a different Jekyll version or need additional dependencies, consider building Jekyll site with GitHub Actions: https://jekyllrb.com/docs/continuous-integration/github-actions/

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