Quick connect: type user@host into Ctrl+K to open a terminal on a machine without saving it

The desktop had no way to reach a machine that was not in the keychain; the phone has had a manual
box on its terminal screen all along. The palette's query now reads as an address when it has an @
in it: a "not saved" row offers to dial it, Enter asks for the password in place, and a second Enter
connects. Escape on the password step goes back to the address.

It goes through the phone's own path, now split out as VaultViewModel.ConnectToEndpointAsync, so the
tab, the host-key question and the connection-log entry are the same on both heads and nothing is
written to the keychain. Password only, as on the phone: a key is the reason to save the host.

The typed row takes the highlight unless a saved host dials exactly that address, so typing a new
address cannot land on a saved machine whose address merely starts the same way.

Covered by eleven new QuickConnectTests; manual check 7.10a covers the real dial.

docs/manual-checks.md

@@ -1388,6 +1388,22 @@ Ctrl+K, then click a result with the mouse rather than pressing Enter.
 
 **Pass:** the palette closes and the connection starts.
 
+### 7.10a Connecting to a machine that is not saved
+
+Ctrl+K, type `user@host` for a reachable machine that is **not** on HOSTS, press Enter, type its password and
+press Enter again. Do it once against a machine whose host key this vault has never seen.
+
+**Pass:** the palette asks for the password in place, with the caret already in the box. On the second Enter
+it closes, a tab named `user@host` opens, and the fingerprint card asks about the key; approving it connects.
+Afterwards HOSTS has nothing new on it, and the connection log has an entry for `user@host:22`. Escape from
+the password box goes back to the address with what was typed still in it.
+
+**Failure means:** a new row on HOSTS is the palette saving what it promised not to. A tab that fails with
+"authentication failed" for a password known to be right is worth comparing against the phone's CONNECT TO A
+MACHINE box, which takes the same path — `VaultViewModel.ConnectToEndpointAsync` — so a difference between
+the two is in how the palette hands the password over, not in the connection. The headless half of this is
+`QuickConnectTests`; what it cannot do is dial.
+
 ### 7.11 A host or a bucket made now can be picked on FILES now
 
 With the files screen's picker open on an empty or short list, go to HOSTS and add a host — or to KEYS and