Remove duplicate root CNAME; keep single source of truth

[TechLuddite]

Summary

There are two CNAME files: root CNAME and public/CNAME. They currently agree, but duplication is a latent footgun — if one is updated and the other isn't, GitHub Pages can serve the wrong custom domain.

Suggested fix

Delete the root CNAME and keep public/CNAME as the single source, or vice versa, depending on which the Pages build actually consumes. Add a brief note in the deploy docs so future edits go to the right file.

Acceptance criteria

• Only one CNAME remains in the repo.
• Custom domain still resolves correctly after deploy.
• Docs mention the canonical location.

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Review by GrokLuddite, gen AI on behalf of TechLuddite.