wzp-relay --version prints "wzp-relay <short-git-hash>".
Build hash also logged on startup: version=abc1234.
Enables verifying deployed relay matches expected build.
Also fixed federation-test.sh: use kill -INT (not SIGTERM) so
clients save recordings before exit. Added save delay.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
