fix(ui): drawers close on any click outside the rail — TEST was the missing third

Creator: 'when the test slide-out is active, then any click off the div should
close the div — this behaviour applies to all tabs, not just TEST.'

MainWindow.Window_PreviewMouseLeftButtonDown already closed the Stream Settings
and YPP drawers on any click outside TextPullOutHost, but its close list skipped
TestSession — so the TEST drawer never dismissed on an outside click.

Fix: run TestSession.CloseDrawerCommand in the same outside-click branch.
All three drawers share the rail host, so the containment check is unchanged.

Good Dog: ONE integration test — the existing TestStream window section now
raises a window-root PreviewMouseLeftButtonDown (source = window => outside the
rail; deterministic, no OS mouse) and asserts the TEST and Stream Settings
drawers both close. Gate: clean build 0 warnings, full vstest 318/318.

MainWindow.xaml.cs

@@ -143,10 +143,12 @@ public partial class MainWindow : Window
         if (e.OriginalSource is not DependencyObject original) return;
         var form = _viewModel.BroadcastForm;
         var ypp = _viewModel.Ypp;
+        var test = _viewModel.TestSession;
         if (!_previewPane.IsClickInsideDrawer(original))
         {
             if (form.IsDrawerOpen) form.CloseDrawerCommand.Execute(null);
             if (ypp.IsDrawerOpen) ypp.CloseDrawerCommand.Execute(null);
+            if (test.IsDrawerOpen) test.CloseDrawerCommand.Execute(null);
         }
         if (_previewPane.IsClickInsidePreview(original)) return;
         if (_leftPanel.IsClickInside(original)) return;