Server.Status() never reports peers, so embedders cannot tell direct from relayed

[Mo3he]

Using tailcat as a library, Server.Status() always returns an empty Peer map, so there is no way for an embedder to tell whether a connected client has a direct path or is going through DERP.

locoBackend.Status() builds its status with the zero value:

func (b *locoBackend) Status() *ipnstate.Status {
	mc := b.sys.MagicSock.Get()
	eng := b.sys.Engine.Get()
	var sb ipnstate.StatusBuilder
	mc.UpdateStatus(&sb)
	eng.UpdateStatus(&sb)
	return sb.Status()
}

ipnstate.StatusBuilder.WantPeers therefore defaults to false, and both producers skip peers in that case: magicsock.(*Conn).UpdateStatus wraps its peerMap.forEachEndpoint loop in if sb.WantPeers, and wgengine's UpdateStatus does the same for st.Peers. So AddPeer is never called and Status().Peer is always empty.

Confirmed against a live server with a connected client: Status().Peer is empty while traffic is flowing.

The useful data is already populated by ep.populatePeerStatus(ps) (CurAddr, Relay), it just never reaches the caller.

Why it matters: I am embedding tailcat in an app that forwards a device's ports, including RTSP. On a relayed path video is effectively unusable, so surfacing direct vs relayed to the operator is the difference between a quick diagnosis and a support ticket. I have worked around it by tracking connections myself from RemoteAddr(), but that cannot distinguish path type.

Happy to send a patch if you will say which shape you would prefer: setting WantPeers: true unconditionally, or a separate opt-in accessor so the default Status() stays cheap.

Related: #39.