feat(studio): timeline inline expansion + __clipTree runtime primitive

When a child element inside a sub-composition is selected, the timeline
replaces the parent scene clip with the deepest-level siblings. Deselect
or selecting outside collapses back. Expanded clips are fully editable —
move, resize, delete, and split — addressed by their real DOM id with
timeline time rebased onto the sub-comp they live in.

Runtime:
- New window.__clipTree API: a read-only hierarchical ClipNode tree
  (id/parentId/children + backing element) so Studio can derive
  parent/child relationships for inline expansion.

Studio:
- useExpandedTimelineElements derives the expanded view from
  selectedElementId + clipParentMap (pure useMemo, no useEffect).
  Each child rebases onto its immediate sub-comp host (start +
  sourceFile), so multi-level nesting targets the right file.
- NLELayout routes expanded-clip edits through the same handlers
  top-level clips use, in local coordinates — edits save to the
  sub-comp source and reflect via reloadPreview (no separate DOM-patch
  path). This is the canonical update; there is no reactive observer.
- findMatchingTimelineElementId resolves sub-comp children with no
  top-level element to `sourceFile#id`.
- Razor tool enabled by default; studio_razor_split analytics event
  fired on single and split-all.
- O(n²) isElementGsapTargeted extracted to gsapTargetCache.ts with a
  cached Set+WeakSet O(1) lookup.

packages/studio/src/player/components/TimelineClip.tsx

@@ -102,7 +102,7 @@ export const TimelineClip = memo(function TimelineClip({
       onDoubleClick={onDoubleClick}
       onContextMenu={onContextMenu}
     >
-      {/* Left accent stripe */}
+      {/* Left accent stripe — wider + brighter for expanded sub-comp children */}
       <div
         aria-hidden="true"
         style={{
@@ -110,9 +110,9 @@ export const TimelineClip = memo(function TimelineClip({
           left: 0,
           top: 0,
           bottom: 0,
-          width: 3,
+          width: el.expandedParentStart !== undefined ? 4 : 3,
           background: trackStyle.accent,
-          opacity: isSelected ? 0.7 : 0.3,
+          opacity: el.expandedParentStart !== undefined ? 0.8 : isSelected ? 0.7 : 0.3,
           borderRadius: `${theme.clipRadius} 0 0 ${theme.clipRadius}`,
           zIndex: 2,
           pointerEvents: "none",