listDrivePeers only checked PeerCapabilityTaildriveSharer, which is
usually granted to a whole group or tag, so it returned most of the
tailnet including offline peers and peers with no reachable peerAPI.
Apply the same conjunction as LocalBackend.driveRemotesFromPeers.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>