Deploy current main to GitHub Pages automatically

[beanbean9339]

Summary

• Build and deploy the Vite dist artifact to GitHub Pages on every push to main, with a manual trigger available.
• Run tests and root metadata validation before publishing.
• Document the one-time Pages setting change and retain the existing gh-pages branch until the first successful workflow deployment.

Tracks #73 for the Pages source switch and live deployment verification. Keep that issue open until the deployed site updates automatically.

One-time setting after merge

In Settings > Pages > Build and deployment > Source, select GitHub Actions. The current legacy branch-based Pages source uses gh-pages; a GITHUB_TOKEN push to that branch does not reliably trigger a Pages rebuild, so this PR uses the official artifact deployment actions instead.

Validation

npm run test (104 passed), npm run validate:metadata (passed), npm run build (passed).

[beanbean9339]

Tracking issue: #73. This PR adds the automatic Pages deployment workflow; #73 stays open for the one-time Pages source switch and verification that a later push to main updates the live site.

[egrace479]

There seem to be a few redundancies here with the ci workflow. Small note: the pages related actions have newer versions, so suggested those.