- extractPeaks scans every frame (was ~1/10) so live decode matches the
  WaveformGen offline output exactly and the shape is stable across counts.
- samples default 256 → 1800 (live-decode source resolution; cost-neutral with
  the full scan; keeps wide/high-DPI waveforms crisp). Override via samples /
  data-samples. index.d.ts synced.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>