fix: buddy images bundled locally instead of jsdelivr CDN

jsdelivr CDN is unreliable in some network environments (China VPN),
causing broken avatar images. All 17 fluent emoji PNGs (600KB total)
are now served from public/buddy/ as static assets.

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

Author: 7418