feat(frontend): lazy-load images, add lightbox viewer, polish AI panel
- Add loading=lazy + decoding=async to all <img> (message card preview,
attachments grid, image grid, avatars via ui/avatar)
- New Lightbox component: fullscreen image viewer with keyboard nav
(←/→/Esc), counter, click-to-close; wired into messages page + detail
- Attachments grid: click image to open, image counter badge, grouped
non-image attachments
- AI analysis panel: line-clamp-3 with Show more/less toggle
- Message card: preview image is now a clickable button opening detail
asepharyana
03d59f0738