Add GitHub Actions workflow for CI and GitHub Pages deployment

[pcottle]

Motivation

• Provide continuous integration on PRs and pushes to main and enable automated deployment to a github-pages branch for GitHub Pages hosting.
• Ensure consistent Node environment and dependency handling using Node.js 18 and Yarn Classic across CI and deploy runs.
• Prevent concurrent workflows for the same ref and allow manual runs via workflow_dispatch.

Description

• Added .github/workflows/pages-deploy.yml to register a workflow that runs on pull_request and push to main and supports workflow_dispatch.
• Added a verify job that checks out the code, sets up Node.js 18, installs Yarn Classic, runs yarn install --frozen-lockfile, and executes yarn gulp build (tests + lint + build).
• Added a deploy job (dependent on verify) that runs only on pushes to main, builds production assets, and deploys the repository tree to the github-pages branch using peaceiris/actions-gh-pages@v4 with publish_dir set to . and force_orphan: true.
• Configured workflow permissions (contents: write) and concurrency grouping with pages-${{ github.ref }} to cancel in-progress runs for the same ref.

Testing

• CI is configured to run yarn gulp build (which includes tests, lint, and build) in the verify job for PRs and pushes to main to validate changes.
• No workflow runs were executed as part of this change in the repository at the time of the PR creation.

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Codex Task

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Publish build output instead of repository root

On GitHub Actions runners CI=true, and gulp build writes the entry page to build/index.html (see gulpfile.js around lines 114-116) rather than creating a root index.html. Deploying publish_dir: . therefore pushes a tree whose root has no generated index page, so GitHub Pages can serve a 404 or stale content from previous commits. Point publish_dir at build (or change the CI build output path) so the generated site root is what gets published.

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