feat: add small ACE Studio upsell link under compose box

fix: cap max duration at 2min (remove 3min option)

fix: hide broken community thumbnails (CDN propagation delay)

fix: Mp4Muxer name collision (self-shadowing destructure)

feat: fast MP4 video generation via WebCodecs + mp4-muxer

style: replace play/pause emoji with SVG icons

style: community share icon 16x16

feat: video download for output + community songs

style: remove left col padding-top

style: sticky top:0 with padding-top for gap

ace-step-jam: AI music generation studio

feat: ACE-Step Studio — custom frontend for ACE-Step v1.5 music generation