Foundation for placing Mixamo skeletal-animation clips on the timeline as
stacked lanes under character objects, alongside the existing keyframe tracks.
- ClipStrip / ClipLane types; TimelineData gains a `clipLanes` array (only the
clip reference + placement is serialized — the AnimationClip is resolved and
retargeted from sourceMediaId at runtime).
- TimelineController: addClipLane / moveClipLane / removeClipLane / clipLanesFor,
create()/loadTimeline() init + backfill clipLanes, emitChanged carries them.
- TimelineChangedEvent → store mirror (timelineClipLanes) via EngineStoreBridge.
- Persistence rides the existing timeline save/load (getTimeline/loadTimeline).
Tanish Manku
5c2fbbc9f3