fix: require Docker Compose v2 in scripts and docs

compose 1.29.2 aborts with KeyError: 'ContainerConfig' against Docker 28,
which broke the deploy on the prod VM.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/migrate-host-nginx.sh

@@ -40,4 +40,4 @@ ss -tlnp | grep -E ':(80|443)\s' && { echo "Ports 80/443 are still busy — insp
 echo "Ports 80 and 443 are free."
 echo ""
 echo "Backup: ${BACKUP_DIR}"
-echo "Next: cd /srv/elevenlabs && docker-compose pull && docker-compose up -d"
+echo "Next: cd /srv/elevenlabs && docker compose pull && docker compose up -d"