docs: document GitHub Pages deployment

[TheAmericanMaker]

Summary

• replace stale Namecheap cPanel deployment instructions with the repository's actual GitHub Pages flow
• document the main/repository-root Pages source and codecarto.dev CNAME
• remove references to nonexistent cPanel launch artifacts and .htaccess

Verification

• CODECARTO_UPSTREAM=/home/jamessesler/Documents/Github/CodeCartographer npm test
• git diff --check
• confirmed via the GitHub Pages API that the site deploys from main at /(root), uses codecarto.dev, and enforces HTTPS