Rebuild CODA on Stable Audio 3 Small Music

Rebuild CODA around a working continuation engine; strip the scope creep

Tests track the window-safe planner; add energy-guard + re-roll coverage; pin transformers to the GPU-verified 4.57.6

UI elevation: live waveform painting, streaming lyrics, vinyl poster v2

Pure audio continuation: drop text pull, add vocal gate + mastering pass

Max out audio context (20s prompt), equal-gain seam, generate() logging

Fix generic "8-bit" output: fp32 conditioning, 15s audio prompt, song-arc structure

Fix music continuation: chained 60s+ generation, native-rate stitching, seamless crossfade