Migrate CI from Travis CI to GitHub Actions

[Copilot]

Travis CI configuration replaced with native GitHub Actions workflow.

Changes

• Added .github/workflows/ci.yml

  • Ruby 3.2 with bundler caching
  • Jekyll build → HTMLProofer validation
  • Artifact upload for built site (7-day retention)
  • Explicit contents: read permission

• Removed .travis.yml

• Updated .gitignore to exclude Jekyll/bundler artifacts (_site/, vendor/, .bundle/, Gemfile.lock)

• Updated README.md badge URL

Workflow Configuration

jobs:
  build-and-test:
    runs-on: ubuntu-latest
    permissions:
      contents: read
    steps:
      - uses: actions/checkout@v4
      - uses: ruby/setup-ruby@v1
        with:
          ruby-version: '3.2'
          bundler-cache: true
      - run: bundle exec jekyll build
      - run: bundle exec htmlproofer ./_site --disable-external

Maintains existing validation while leveraging GitHub Actions caching and artifact features.

Original prompt

Move away from external travis to built-in GitHub actions. Also do we need linting and other required CI/CD scripts/commands that are currently missing?

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