Merge branch 'main' into claude/vault-unlock-logout-autosync-a84c35

Four files needed a hand, and all four were two branches adding something in
the same place rather than either changing what the other did.

The shell's constructor now takes both new parameters: main's SFTP session
factory, which it must have because it builds the transfers view model, and
this branch's optional resume handler, which stays last so every existing test
that constructs a shell without one still gets a shell that can only be online
because somebody signed in during this run. App.axaml.cs, ShellFlowTests and
QuickConnectTests pass the pair; the layout suite keeps both of its new fields.

Signing out now detaches the transfers screen exactly as locking does, and the
confirmation says that an open transfer session survives it. That is the same
policy both sides already argue for their own case: signing out destroys this
machine's copy of the vault, not work that authenticated before it.

QuickConnectTests did not compile on main — the SFTP commit added a constructor
parameter and the quick-connect suite, merged from a parallel branch just
before it, was still calling the old one. Fixed here rather than worked around,
since the merged tree has to build.

dotnet build, dotnet test and dotnet format --verify-no-changes are all clean:
980 tests, including the end-to-end suite against real containers.

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

@@ -41,6 +41,15 @@
       </StackPanel>
     </Border>
 
+    <!--
+      The other thing that outlives signing out, on the same reasoning and worth its own line because it is
+      a connection this machine holds rather than a window it shows: a transfer in flight authenticated
+      before any of this and keeps writing into its part file afterwards.
+    -->
+    <TextBlock Classes="hint" FontSize="11" TextWrapping="Wrap"
+               IsVisible="{Binding Transfers.IsConnected, FallbackValue=False}"
+               Text="A file-transfer session is open on this machine. Signing out does not close it either — it goes when DodoSSH does." />
+
     <StackPanel Orientation="Horizontal" Spacing="8">
       <Button Classes="danger" Content="SIGN OUT AND DELETE"
               Command="{Binding ConfirmSignOutCommand}" IsEnabled="{Binding !IsBusy}" />