Retired GitHub Pages documentation

GitHub Pages was the original host for the Stowplan documentation. The canonical site now uses the assets-only Cloudflare Workers deployment at the same docs.stowplan.lasers.app hostname.

Do not enable Pages as a second publisher for the canonical hostname. During an emergency rollback before the Pages site is deleted, detach the Workers Custom Domain and restore the unproxied docs.stowplan.lasers.app CNAME to j-256.github.io. After Pages retirement, use a previous stowplan-docs Worker deployment instead.

The release gate continues to build the docs with both /stowplan/ and / bases, so a fork may choose GitHub Pages or another project-subpath static host without changing documentation source links.