[Feature]: Add pause/play control to contributor carousel

[FrankezeCode]

Problem or opportunity

The landing page contributor carousel auto-rotates every 4 seconds. Add a pause/play toggle so visitors can read names and GitHub links without the carousel moving away.

Proposed solution

• Add a Pause / Play button below the contributor carousel
• Clicking Pause stops auto-rotation; Play resumes it
• Button has clear label and aria-pressed state
• Existing prefers-reduced-motion behavior is preserved
• Only src/components/landing/contributor-carousel.tsx changed (unless tiny shared utility is justified)
• No unrelated file changes

HOW TO TEST

1. Run npm run dev and scroll to the Network section on /
2. Confirm carousel auto-rotates by default
3. Click Pause — rotation stops; center name stays visible
4. Click Play — rotation resumes
5. Enable “Reduce motion” in OS settings — confirm auto-rotate does not run (or behaves per existing hook)
6. Run npm run build — passes

Alternatives considered

No response