HPSS margins — pull the sine out of the clicks

HPSS splits a sound into its sustained part and its hits — watch a steady tone go one way and the clicks go the other, then A/B the split by ear. The material: a sustained 440 Hz sine (harmonic) + 8 Hz click train (percussive), STFT 1024/256, decompose.hpss at margins 1/2/4/8. Per-margin spectrogram rows show mixture / harmonic / percussive — the horizontal 440 Hz line must live in H, the vertical click stripes in P. Badges assert the margin-1 identity max|S−(H+P)| < 1e-5, energy capture (H keeps >90% of the 440 Hz bin with <10% of click energy, and vice versa), and that H's click-leak share drops below −30 dB by margin 4. A/B buttons play the istft'd components against the mix. Numerics node-verified.