refactor(js): fix layout transition handling and initialization (#5956)

- Fix broken holdTransition timer (local var → instance property)
- Remove duplicate resize listeners registered on every call
- Consolidate layout initialization to layout.ts only
- Move app-loaded class to layout.ts Data API section

Based on PR #5956 by @dfsmania.

Co-Authored-By: Diego Smania <diego.smania@gmail.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people