Update app.py

perf: remove concurrency_limit on create API

feat: add small ACE Studio upsell link under compose box

perf: in-memory feed cache — load once at startup, append on upload, zero disk reads

Revert "perf: single index.json for community feed (1 read vs N meta.json reads)"

perf: single index.json for community feed (1 read vs N meta.json reads)

fix: check actual thumb.png file instead of has_thumb metadata flag

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

style: blue gradient + headphones emoji for Space card

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