Compress team avatars to under 25KB; roster cleanup

- Re-encode 134 member avatars in place (JPEG/PNG/WEBP; formats and filenames preserved); all now <=24.4KB, ~21MB saved
- Remove Guangjun Xu from roster and delete orphaned photo
- Delete 6 unreferenced duplicate avatar files
- team-data.js also carries existing year/destination edits

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: xpqiu