Of note, this test scene still doesn't use the new footer properly.
Should these even be here? Maybe it's better to leave these real world
flows to a `Navigation` style test so we're not dealing with weird test
setups that kinda do something but don't... or maybe do it in three
different ways (two footers present, three back buttons etc.)
Dunno. But this kind of covers what I want (except it doesn't cover the
new footer usage).
I believe once upon a time the `SelectedRoom` bindable used to be bound
to `RoomManager.JoinedRoom` or similar. But now it's effectively private
to the lounge subscreen and so a lease is unnecessary.