Build the site from one source and deploy it to both hosts from GitHub
Actions, so neither depends on a host's default Jekyll toolchain.
- Gemfile/Gemfile.lock pin Jekyll 4.4.1 on Ruby 3.4; both workflows use
them, which keeps the two sites on an identical toolchain
- _config.yml carries the GitHub Pages url and baseurl, fixing asset
paths that previously resolved off-site; _config.cloudflare.yml layers
over it for the pages.dev root
- wrangler.jsonc declares the Pages project name and output directory
- 404.html gives both hosts a page for unmatched routes
- exclude README.md from the output and stop shipping CSS sourcemaps
