refactor(ui): remove the stale-worker banner

The banner compared the running worker's build SHA against the
selected list's HEAD via a git ancestor check on every list switch
and reconnect. It added a git-rev-parse MSBuild target, a hub call,
and a poll loop for a corner case that hasn't come up in practice —
not worth the moving parts.

src/ClaudeDo.Ui/Views/MainWindow.axaml

@@ -259,29 +259,6 @@
       </StackPanel>
     </Border>
 
-    <!-- Stale-worker notice — bottom-right corner, above the update popup. Persistent
-         (no auto-dismiss timer): the running worker predates the selected list's merged
-         HEAD, so a restart is needed before "verified" claims against it are trustworthy. -->
-    <Border Grid.Row="0" Grid.RowSpan="3"
-            VerticalAlignment="Bottom" HorizontalAlignment="Right"
-            Margin="0,0,16,100"
-            ZIndex="100"
-            IsVisible="{Binding IsStaleWorkerBannerVisible}"
-            Background="{DynamicResource DeepBrush}"
-            BorderBrush="{DynamicResource LineBrush}"
-            BorderThickness="1"
-            CornerRadius="6"
-            Padding="14,10">
-      <StackPanel Spacing="8" Width="260">
-        <TextBlock Classes="body" Text="{loc:Tr shell.staleWorker.message}" TextWrapping="Wrap"/>
-        <StackPanel Orientation="Horizontal" Spacing="8" HorizontalAlignment="Right">
-          <Button Classes="btn"
-                  Content="{loc:Tr shell.menu.restartWorker}"
-                  Command="{Binding RestartWorkerCommand}"/>
-        </StackPanel>
-      </StackPanel>
-    </Border>
-
     <!-- External merge popup card — bottom-left corner, while an MCP session owns an
          unresolved unit-merge conflict. Does not auto-dismiss; stays until the merge ends. -->
     <Border Grid.Row="0" Grid.RowSpan="3"