feat: add emoji update script, refresh apple/google/twitter emoji data

- New scripts/update-emoji.js downloads from emoji-datasource CDN
  (jsdelivr) with concurrency pool, atomic writes, incremental updates
- Updated apple (3624→3781), google (3623→3781), twitter (3624→3781)
- Removed dead downloadEmoji function (old S3 CDN returns 403)
- joypixels and blob kept as-is (not on emoji-datasource CDN)

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: LyoSU