Adds audio to the scene engine without any third-party/geo-blocked sourcing: the
beds + SFX are synthesized with ffmpeg, so they're license-free (CC0, self-authored)
and need no acquisition — the same play as self-authoring Lottie.
- public/audio/: music-ambient.mp3 (soft 3-tone pad, looped) + sfx-whoosh/pop/chime.
- FlexStory: optional music/musicVolume/sfx props (optional so the existing render
binding needs no change). Renders <Audio loop> for the bed + a whoosh at each
scene start and a chime on the final scene, driven by precomputed scene starts.
- check-assets: now also scans public/audio (+ lottie) with folder-prefixed keys;
assets.json ledgers the 4 audio files (CC0 self-authored).
Verified: tsc clean; a 6s FlexStory render produces an MP4 with a real audio stream
(ffprobe: codec_type=audio). NOTE: these are placeholder/SFX-grade; a premium
curated music library (by vibe) is a separate sourcing sweep, and the studio music
picker → FlexStory `music` prop is a follow-up wiring.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>