Add StammbaumAffordance: a touch-only "drag to explore · pinch to zoom" hint
that auto-dismisses on the first canvas pointer interaction (wired via the
gesture action's onGestureStart) or the explicit close, and stays dismissed for
30 days via a localStorage timestamp (boolean gate only, never rendered).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
