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/gsapScriptCommitHelpers.ts

@@ -37,6 +37,13 @@ function isRecord(value: unknown): value is Record<string, unknown> {
   return typeof value === "object" && value !== null;
 }
 
+export function formatFieldsSuffix(rawFields: unknown): string {
+  const fields = Array.isArray(rawFields)
+    ? rawFields.filter((f): f is string => typeof f === "string")
+    : [];
+  return fields.length > 0 ? ` (${fields.join(", ")})` : "";
+}
+
 export async function readJsonResponseBody(res: Response): Promise<unknown> {
   const contentType = res.headers.get("content-type") ?? "";
   if (!contentType.includes("application/json")) {
@@ -55,14 +62,10 @@ function formatGsapMutationHttpErrorMessage(statusCode: number, body: unknown):
 export function formatGsapMutationRejectionToast(error: GsapMutationHttpError): string {
   const body = error.responseBody;
   if (isRecord(body)) {
-    const fields = Array.isArray(body.fields)
-      ? body.fields.filter((field): field is string => typeof field === "string")
-      : [];
-    const suffix = fields.length > 0 ? ` (${fields.join(", ")})` : "";
     return `Couldn't save animation: ${formatGsapMutationHttpErrorMessage(
       error.statusCode,
       body,
-    )}${suffix}`;
+    )}${formatFieldsSuffix(body.fields)}`;
   }
   return `Couldn't save animation: ${error.message}`;
 }