feat: migra para GitHub Pages (thiagoprazeres-ufpe)

- .github/workflows/deploy-pages.yml — GH Actions Pages
- vite base path '/design-system-ufpe/' em produção
- Plugin Penpot empacotado em /plugin/ no mesmo deploy
- URLs Cloudflare (.pages.dev) → GitHub Pages (github.io)
- Remove .gitlab-ci.yml + .cloudflare/
- README + ROADMAP atualizados (CI = GH Actions, Repo = GitHub)
- generate-build-info.js aponta para GitHub
- Links GitLab → GitHub (/-/issues → /issues, /-/commit → /commit)

GitLab fica como mirror.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>