fix(studio): keep Timeline under the 600-line cap and un-export postRootDurationToPreview

CI file-size check and fallow audit caught two issues the --no-verify
commits skipped: Timeline.tsx sat at 602 (max 600) and
postRootDurationToPreview was an unused export (only called in-file).
Trim a comment to hit 600; drop the export.

packages/studio/src/hooks/timelineEditingHelpers.ts

@@ -190,7 +190,7 @@ export function patchIframeDomTiming(
   }
 }
 
-export function postRootDurationToPreview(
+function postRootDurationToPreview(
   iframe: HTMLIFrameElement | null,
   durationSeconds: number,
 ): void {

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

@@ -230,9 +230,7 @@ export const Timeline = memo(function Timeline({
     setRangeSelectionRef,
   });
 
-  // basisDuration drives the zoom (committed, no live preview); effectiveDuration
-  // adds the active drag/resize preview so the ruler/width follow a past-end drag.
-  // See timelineLayout for why the split prevents jump-during-extend.
+  // basis drives the zoom (committed); effective adds the live preview (see timelineLayout).
   const basisDuration = useMemo(
     () =>
       computeTimelineBasisDuration(