Generates a GitHub Pages deploy workflow for this site.
Usage
mix cherry.gen.action [--source DIR] [--branch NAME] [--force] [--json]Writes .github/workflows/pages.yml: build on push to --branch
(default main), upload the site, deploy via GitHub's Pages actions.
The workflow adds .nojekyll, and a CNAME when the site's url is a
custom domain (skipped for *.github.io and subpath base_path sites).
One-time repo setup: Settings → Pages → Source → GitHub Actions.