fix(ui): show a banner when a ConPTY session dies after startup

InteractiveTerminalViewModel.HasExitedAfterStartup now covers every
post-startup death that ExitedAfterStartup alone missed (crash, clean
exit, quiet exit inside the grace window) -- previously the tile just
stayed looking alive/thinking with zero signal. ConPtyPaneView binds a
new banner to it (message + Retry + Close); CanRetry simplifies to
"any HasExited state" since the same descriptor factory can relaunch
either kind of death. HandlerRestartCoordinator's worker-side
auto-restart path is untouched.

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

@@ -55,6 +55,27 @@
         </Grid>
       </Border>
 
+      <!-- Session-ended banner: process died without a start-failure already covering it -->
+      <Border DockPanel.Dock="Top"
+              IsVisible="{Binding Terminal.HasExitedAfterStartup}"
+              Background="{DynamicResource ErrorTintBrush}"
+              BorderBrush="{DynamicResource BloodBrush}"
+              BorderThickness="0,0,0,1" Padding="12,6">
+        <Grid ColumnDefinitions="*,Auto,Auto">
+          <TextBlock Grid.Column="0" Classes="meta" Text="{Binding ExitedBannerText}"
+                     Foreground="{DynamicResource BloodBrush}"
+                     TextWrapping="Wrap" VerticalAlignment="Center" />
+          <Button Grid.Column="1" Classes="btn" Margin="12,0,0,0"
+                  Content="{loc:Tr missionControl.retry}"
+                  ToolTip.Tip="{loc:Tr missionControl.retryTip}"
+                  Command="{Binding RetryCommand}" />
+          <Button Grid.Column="2" Classes="btn" Margin="12,0,0,0"
+                  Content="{loc:Tr missionControl.closeSession}"
+                  ToolTip.Tip="{loc:Tr missionControl.closeSession}"
+                  Command="{Binding CloseCommand}" />
+        </Grid>
+      </Border>
+
       <!-- Embedded ConPTY terminal, with a starting overlay until the session is spawned -->
       <Panel>
         <views:InteractiveTerminalView DataContext="{Binding Terminal}" />