Live edit-while-playing: just-in-time scheduler

Play now uses playLive(): Csound runs with `f 0` keeping it alive; a JS lookahead scheduler injects each section's events ~1.5s before they play via inputMessage, reading the CURRENT state each tick (absolute score-time seconds, no t-tempo).

• Both deferred features now done (SFX channel + live editing).

Verified: with Puppeteer: audio flows (RMS 0.19), 314 events injected, and a section toggled drums-off -> open mid-playback emitted 81 drum events at its scheduled time (the live edit applied).

▶ Play it: Barometric Stampede — the genre that is mostly drums, so the kit has nowhere to hide https://stellate.app/?genre=jungle&seed=2443&path=1718.20504,1737.20537,1699.20537&xdur=13.122

c3adf86 https://github.com/aboard-io/stellate/commit/c3adf86b956ce1b92b6d0f589e18b6bf3c98bc0b