Default is smooth (lerp each point between adjacent frames); a motion:step
toggle preserves the snap-to-frame behaviour. Points missing in either
adjacent frame are hidden during the transition to avoid pop-in.
- /compare page renders two ortho-camera panels fed by /api/runs/{stem}/frames.json
- shared controls: play/pause, scrubber, speed (0.5-4x), axes sync (independent/locked)
- linked hover: picks nearest point in one panel, highlights matching point_id in other
- add/remove-jitter nulls handled via per-frame packed positions + setDrawRange
- independent error states per panel; theme-aware colors via themechange event
