fix: resolve metadata URL and remove raw HTML

[telemarkdigital-publisher]

Summary

• Resolves metadataBase from NEXT_PUBLIC_SITE_URL or Vercel's deployment URL instead of hardcoding localhost.
• Adds root canonical and Open Graph URL metadata.
• Replaces the landing-page dangerouslySetInnerHTML with equivalent JSX.
• Enables react/no-danger and adds unit coverage for metadata URL resolution and the raw-HTML guard.

Closes #1
Closes #2

Verification

• npm test
• npm run lint
• npm run build
• git diff --check

Notes

• I kept the metadata change focused because PR feat: add SEO metadata and structured data #81 already covers broader SEO infrastructure for ops: add sitemap.xml, robots.txt, and structured data #66.

[joelpeace48-cell]

@telemarkdigital-publisher ci fails, please fix it

[telemarkdigital-publisher]

Thanks for the heads-up. I pushed a narrow CI/accessibility fix in 716ffb5.

The failing axe rule was scrollable-region-focusable on the wide chart plot in /operators under the mobile Safari project. The chart frame now gives wide scrollable plots keyboard focus and a visible focus outline, so the horizontal scroll region is reachable without a pointer.

Verification run locally:

• npm test
• npm run lint
• npm run build
• npx playwright test e2e/accessibility.spec.ts --project=chromium --grep operators

I could not run the local mobile-safari project on this Windows workspace because the local Playwright WebKit browser is not installed here, but the same axe failure path should rerun in CI on the refreshed branch.