ci: publish CNAME on every GitHub Pages deploy

[Copilot]

GitHub Pages loses the custom domain (graphr.prasenjit.net) on each deploy because no CNAME file is included in the published artifact, requiring manual re-entry after every release.

Change

• .github/workflows/cd-pages.yml — added the cname parameter to the peaceiris/actions-gh-pages@v4 step:

- name: Deploy to gh-pages branch
  uses: peaceiris/actions-gh-pages@v4
  with:
    github_token: ${{ secrets.GITHUB_TOKEN }}
    publish_dir: ./dist
    publish_branch: gh-pages
    force_orphan: true
    cname: graphr.prasenjit.net   # ← added

The action natively handles this parameter by writing a CNAME file at the root of the gh-pages branch on every push, so the custom domain persists across deployments without any manual intervention.

Original prompt

Update the GitHub Pages deploy workflow so that every build publishes a CNAME file with the custom domain.

Repo: prasenjit-net/graphr
Branch: main
Workflow file to modify: .github/workflows/cd-pages.yml

Requirements:

• Ensure the workflow (or build step) creates a CNAME file containing exactly:
  graphr.prasenjit.net
• The CNAME file must end up in the published Pages artifact / gh-pages content so it is not overwritten on subsequent builds.
• Do not change the domain.
• Keep other behavior of the workflow intact.

Deliverables:

• A PR against main with the workflow change.
• If needed, add or update build steps so the CNAME is generated during the build (not manually committed).

This pull request was created from Copilot chat.

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