Proof-of-concept for the repo hierarchy migration:
- Move the five z-governance* pages into app/governance/ (folder index
  for the overview, so /governance/, /governance/meetings/, etc.).
- Replace the Governance separator + flat entries with a single
  collapsible folder; add app/governance/_meta.js for section order.
- Enable collapsible sidebar groups via Layout sidebar config
  (defaultMenuCollapseLevel + autoCollapse).
- Add public/_redirects (GitLab Pages) mapping old flat slugs -> new
  paths so external links survive.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>