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/useResolvedTimelineEditCallbacks.ts

@@ -0,0 +1,30 @@
+import { useMemo } from "react";
+import { useTimelineEditContext } from "../../contexts/TimelineEditContext";
+import type { TimelineEditCallbacks } from "./timelineCallbacks";
+
+// Props a parent (e.g. NLELayout) may pass to <Timeline> to intercept edits —
+// the rest of the callback bag still comes from TimelineEditContext.
+export type TimelineEditOverrides = Pick<
+  TimelineEditCallbacks,
+  "onMoveElement" | "onResizeElement" | "onBlockedEditAttempt" | "onSplitElement"
+>;
+
+// Merge any prop overrides over the context callbacks. Used so NLELayout can
+// wrap move/resize/split (to rebase expanded sub-comp clips) while every other
+// callback falls through to the context unchanged.
+export function useResolvedTimelineEditCallbacks(
+  overrides: TimelineEditOverrides,
+): TimelineEditCallbacks {
+  const ctx = useTimelineEditContext();
+  const { onMoveElement, onResizeElement, onBlockedEditAttempt, onSplitElement } = overrides;
+  return useMemo(
+    () => ({
+      ...ctx,
+      onMoveElement: onMoveElement ?? ctx.onMoveElement,
+      onResizeElement: onResizeElement ?? ctx.onResizeElement,
+      onBlockedEditAttempt: onBlockedEditAttempt ?? ctx.onBlockedEditAttempt,
+      onSplitElement: onSplitElement ?? ctx.onSplitElement,
+    }),
+    [ctx, onMoveElement, onResizeElement, onBlockedEditAttempt, onSplitElement],
+  );
+}