fix(ui): keep ConPTY sessions alive across Mission Control layout rebuilds

TerminalView kills its child process on any logical-tree detach unless
BeginReparent() suppressed it, and RebuildOverviewGrid() detaches every
existing pane whenever one is added - so opening a second interactive
session killed the first. Focus-mode tab switches had the same defect.

PtyTerminalSession now puts the control in permanent reparent mode after
launch (teardown stays explicit via ConPtyPaneViewModel.Dispose -> Kill),
and the new ConPtyPaneHost reparents each pane's single long-lived view
across grid rebuilds and tab switches instead of letting the DataTemplate
instantiate a dead replacement.

src/ClaudeDo.Ui/Views/MissionControl/MissionControlView.axaml

@@ -8,8 +8,11 @@
              x:DataType="vm:MissionControlViewModel"
              x:Class="ClaudeDo.Ui.Views.MissionControl.MissionControlView">
   <UserControl.DataTemplates>
+    <!-- ConPtyPaneHost reuses the pane's one long-lived view across layout rebuilds and
+         tab switches — instantiating ConPtyPaneView here directly would detach (and, without
+         reparent suppression, kill) the running session every time a pane is added. -->
     <DataTemplate DataType="vmm:ConPtyPaneViewModel">
-      <mc:ConPtyPaneView Margin="6" />
+      <mc:ConPtyPaneHost Margin="6" />
     </DataTemplate>
   </UserControl.DataTemplates>
   <DockPanel LastChildFill="True" Background="{DynamicResource VoidBrush}">