Open a thread's linked dev servers from mobile

[jakeleventhal]

Desktop shows a thread's linked dev servers with a globe on the sidebar row and in the in-app browser. Mobile does not subscribe to that discovery stream, so a phone cannot reach a server the thread already started.

Show those servers on the thread row and in the thread header. Rewrite loopback addresses onto the environment's connection host so LAN and tailnet servers open. List tunnel-only servers as unreachable instead of opening a dead page. iOS can use a menu of every server; Android's in-flow header can open the first reachable one.

#8562 implements this and was closed pending agreement on those controls and connection modes.