0.46.0 — walk mode

Soundwalk support: segment-first analysis of moving recordings.

• New ambiscape walk: sub-soundscape zones from multivariate change-point
  detection on the cached 1 Hz features, per-zone descriptors, step cadence
  (walking-speed proxy + self-noise salience), figure-ground regime labels,
  route-profile figure.
• Non-stationarity diagnosis in every summary; multi-regime sessions say so
  in their README where the averages are printed.
• Draft keynote regimes split on spectrum, not level alone; PANNs tag budget
  is now --max-tags.
• Schaeffer map attributes detected events to covering named spans; the
  Schafer timeline draws the soundmark edge the map already had.
• Soft low-confidence descriptors carry a dagger and footnote in the README
  table.

See CHANGELOG.md for details. Grew out of the first soundwalk analysed with
the toolbox (Blindern campus, 2026-08-24).