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/hooks/useRazorSplit.ts

@@ -3,6 +3,7 @@ import type { TimelineElement } from "../player";
 import { usePlayerStore } from "../player";
 import { saveProjectFilesWithHistory } from "../utils/studioFileHistory";
 import { getTimelineElementLabel, collectHtmlIds } from "../utils/studioHelpers";
+import { trackStudioRazorSplit } from "../telemetry/events";
 import {
   canSplitElement,
   buildPatchTarget,
@@ -196,6 +197,7 @@ export function useRazorSplit({
         });
 
         reloadPreview();
+        trackStudioRazorSplit({ mode: "single", count: 1 });
         showToast(`Split ${getTimelineElementLabel(element)} at ${splitTime.toFixed(2)}s`, "info");
         if (skippedSelectors?.length) {
           showToast(
@@ -277,6 +279,7 @@ export function useRazorSplit({
         });
 
         reloadPreview();
+        trackStudioRazorSplit({ mode: "all", count: splitCount });
         showToast(`Split ${splitCount} clips at ${splitTime.toFixed(2)}s`, "info");
       } catch (error) {
         const message = error instanceof Error ? error.message : "Failed to split clips";