Add hackathon #1 recap with photos and updated guide

- Restructure hackathon page: recap at top, reusable guide below
- Add 7 optimized event photos + cropped cover image (date removed)
- Stats: 70+ attendees, 8 PRs, 468 stars, 5 tracks
- Table of submitted skills with authors
- "Join the next one" section for future hackathons
- YouTube recording placeholder

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: manuelcorpas