The M0 pilot mis-membered the waveform data pipeline into features/waveform,
creating a core->feature inversion: ~12 audio-core files in store/ imported
refreshWaveformForTrack / fetchWaveformBins / bumpWaveformRefreshGen from the
feature barrel. These are playback coordination (write waveformBins into
playerStore on track change, last-write-wins gen guard), not seekbar rendering.
Move waveformRefresh + waveformRefreshGen (+ tests) to src/store/ and
waveformParse (+ test) to src/utils/waveform/ (beside waveformSilence). The
feature now holds only the seekbar UI (WaveformSeek/SeekbarPreview + their
hooks/render utils); its barrel exports UI only. Core consumers import the
pipeline directly from @/store/*. Restores the no-core->feature-inversion rule.