Desktop: build only the host cards near the view, with a virtualising wrap panel for the board

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

@@ -577,8 +577,9 @@
                            SelectedItem="{Binding #Board.((vm:VaultViewModel)DataContext).SelectedSidebarRow, Mode=OneWay}"
                            ToolTip.Tip="Double-press a card for a shell. Ctrl or Shift picks out several, and so does a band dragged across the space between them; right-click any of them for what can be done to the set.">
 
+                    <!-- Builds only the cards near the view; see VirtualizingWrapPanel. -->
                     <ListBox.ItemsPanel>
-                      <ItemsPanelTemplate><WrapPanel /></ItemsPanelTemplate>
+                      <ItemsPanelTemplate><views:VirtualizingWrapPanel /></ItemsPanelTemplate>
                     </ListBox.ItemsPanel>
 
                     <!--