- Add responsive card layout for mobile (<640px) as alternative to desktop table
- Desktop: table hidden below sm breakpoint, improved col widths
- Mobile: each file as a card with filename, metadata grid (2x2), public status, actions
- Keep table headers accessible via <caption>
- Fix video seek-bar reset bug: change <template x-if> to x-show so
video/audio elements stay mounted and playback state isn't lost
on Alpine re-render