fix(studio): persist canvas z-order actions correctly for static elements

An adversarial review of the canvas context-menu z-order pipeline (Bring to
Front / Forward / Backward / Send to Back) found the resolver math sound but
the glue between the menu and the commit hook broken:

- The menu optimistically wrote style.zIndex AND position: relative to the
  live elements BEFORE the commit hook ran. The hook decides whether to
  persist position by checking getComputedStyle(el).position === 'static' —
  always false after the pre-apply — so the position patch was never
  persisted on the menu path and the reorder silently reverted at the
  post-commit reload for any nested/static element (root clips survive only
  because the runtime forces position:absolute). The same pre-apply made the
  failure rollback capture the already-mutated values, restoring the broken
  state on persist errors. The menu no longer pre-applies; the hook owns the
  live writes (it already applied both synchronously) and now sees true
  priors. Siblings without a persistable identity still get their z applied
  live-only so a renumber stays visually coherent.
- The commit hook's entry.key store-sync plumbing had zero production
  callers; the store zIndex went stale until full reload. All three callers
  (canvas menu via PreviewOverlays, timeline lane z-sync, LayersPanel) now
  derive and pass the timeline store key (new deriveTimelineStoreKey helper).
- patchElementBatch discarded the server's per-patch matched[]; unresolvable
  siblings persisted partially and silently. Unmatched targets now warn and
  report save-failure telemetry (z-reorder-unmatched) without rolling back
  the matched subset.
- template/noscript elements counted as painting siblings, so renumber
  fallbacks wrote z-index/position into <template> tags in the source file.
  Excluded from the sibling family.
- The default undo coalesce key merged DISTINCT z actions within 300ms into
  one undo entry; the action kind is now part of the key (LayersPanel drags
  keep coalescing within a drag; explicit lane-move gesture keys untouched).
- rectsIntersect comment claimed touching rects intersect; the strict
  inequalities say otherwise — comment fixed.

packages/studio/src/player/lib/timelineElementHelpers.ts

@@ -298,6 +298,25 @@ export function getTimelineElementIdentity(element: { key?: string | null; id: s
   return element.key ?? element.id;
 }
 
+/**
+ * Timeline store key for a z-reorder entry built OUTSIDE the timeline
+ * expansion (canvas context menu / LayersPanel), so the reorder commit can
+ * update the store's zIndex synchronously. Matches buildTimelineElementKey's
+ * stable branches (`sourceFile#domId`, else the selector-based key). Undefined
+ * when the element has neither a DOM id nor a selector — the timeline's
+ * fallback branch needs its own fallbackIndex, which these callers don't have,
+ * so such an entry simply skips the synchronous store update.
+ */
+export function deriveTimelineStoreKey(params: {
+  domId?: string;
+  selector?: string;
+  selectorIndex?: number;
+  sourceFile?: string;
+}): string | undefined {
+  if (!params.domId && !params.selector) return undefined;
+  return buildTimelineElementKey({ id: "", fallbackIndex: 0, ...params });
+}
+
 // ---------------------------------------------------------------------------
 // DOM node querying
 // ---------------------------------------------------------------------------