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.

src/DodoSSH.Client.App/Views/QuickConnect.axaml

@@ -170,7 +170,7 @@
           The second step, in the same card, so the keyboard never leaves the palette: Enter on the address
           comes here, Enter here dials, Escape goes back to the address rather than closing. The box carries
           PasswordChar and nothing is written anywhere — see MainWindowViewModel.IsAskingForAdHocPassword,
-          and VaultViewModel.ConnectManuallyAsync for why a typed password is the only way in.
+          and VaultViewModel.ConnectToEndpointAsync for why a typed password is the only way in.
         -->
         <StackPanel x:Name="PasswordStep" IsVisible="{Binding IsAskingForAdHocPassword}">