Connections: drop the manual box's view-model state now that both heads ask through the prompt

The phone's Connections screen no longer draws the user@host + password box, and the desktop never
did, so nothing bound VaultViewModel.ManualTarget, ManualPassword, ManualStatus or
ConnectManuallyCommand any more, nor MainWindowViewModel.ConnectToRecentCommand, whose address branch
wrote into that box. They are gone, and so is VaultViewModel.AskAboutHost, whose one caller was
ConnectToRecent. TryParseManualTarget, ManualEndpoint and ConnectToEndpointAsync stay: the prompt, the
desktop's Ctrl+K palette and the phone's hosts search all use them. The reasoning the removed members
carried moved onto ConnectToEndpointAsync and ChoosePromptRecentAsync.

The tests whose subject is still live now go through the prompt instead of the box: a typed address
dialled exactly as typed, port 22 by default, the refusal sentences, the host-key retry replaying the
attempt that raised it, the host-key card staying over the surface it was typed on, the session facts
for a typed password, and no forwards for a typed address. The recent-row cases now drive
ChoosePromptRecentCommand. Two cases existing prompt tests already covered were deleted. Manual check
11.8 now describes recent rows landing on the prompt.

docs/manual-checks.md

@@ -2099,14 +2099,16 @@ that dialled it taken away. See `MainWindowViewModel.OnVaultConnectionFailed`.
 With at least one keychain host and one machine connected to by hand in the log, open Connections with
 nothing running.
 
-**Pass:** tapping the keychain one lands on HOSTS with that host **ticked and the action bar up**, ready
-for CONNECT out of the ⋯. Tapping the hand-typed one puts its address back in the box on this screen and
-leaves the password box **empty**. Neither one dials anything on its own.
+**Pass:** tapping the keychain one puts **its name** on the `connect to:` line and carries on as typing that
+name would — its password line, or straight into a terminal for a host with a key or a saved password.
+Tapping the hand-typed one puts its `user@host:port` on the line and asks for its password with the password
+line **empty**. Neither one leaves this screen, and the hand-typed one dials nothing until a password is
+given.
 
-**Failure means:** if the hand-typed one navigates to HOSTS, the log entry is carrying a host id it should
-not have. If the password came back, something is storing it — it never was. And if the keychain one arrives
-at a list with nothing marked, `ConnectToRecent` is setting the selection rather than going through
-`AskAboutHost`: nothing on that list means "selected" any more, so that is a screen with nothing to press.
+**Failure means:** if the hand-typed one shows a host's name rather than its address, the log entry is
+carrying a host id it should not have. If the password came back, something is storing it — it never was.
+And if the keychain one shows the logged address rather than the host's name, the host id is not being
+matched against the keychain — see `MainWindowViewModel.ChoosePromptRecentAsync`.
 
 ### 11.9 The keychain and snippets are the vault's, and back walks out of them