LiveKit v1.12.0 tightens TURN security: credentials now carry a TTL,
and TURN no longer relays to restricted peer CIDRs by default. The
role defaults match upstream's secure defaults and are appropriate
for typical playbook deployments.

Bumps the migration-validation gate accordingly so users are pointed
at the CHANGELOG entry on next run.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>