fix(tests): pass numeric uid/gid for seat-user/seat-group in CI
nixery containers have no /etc/passwd, so users::get_user_by_name("root")
returns None. resolve_user/resolve_group already handle numeric strings,
so pass the current uid/gid directly to avoid the name lookup.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>