[codex] Add self-hosted static docs deploy flow

[morganross]

This PR switches the docs repo toward a self-hosted static deployment flow instead of GitHub Pages.

What changed:

• changes the Docusaurus defaults to build for https://apicostx.com/docs-static/
• updates the PR build workflow to validate with self-host URL settings
• replaces the GitHub Pages deploy workflow with a branch publish workflow that writes built static files to a deploy branch
• adds server-side scripts for pull, verify, publish, and rollback of static docs releases

Why:

• the docs source should stay in GitHub
• GitHub Actions should do the build
• the frontend server should host only the built static files
• GitHub should not need SSH access to the frontend server

Impact:

• main remains the source branch
• gh-pages becomes the built static branch the frontend server can pull
• the first intended self-host test path is /docs-static/
• the repo now includes the server-side script templates needed for a pull-based deploy

Validation:

• checked the repo diff scope before staging
• shell scripts pass bash -n
• did not run a full end-to-end GitHub Actions deploy from this environment
• did not configure Apache or the live frontend server path yet

Root cause addressed:

• the existing repo was still set up for GitHub Pages as the final host, but the desired architecture is GitHub for source/build and the frontend server for serving built static output

[morganross]

Closing this because the repo is using a direct-push workflow and the changes are already on main.