fix(ui): enforce continuous rounded window corners

MainWindow.xaml

@@ -353,7 +353,7 @@
     </shell:WindowChrome.WindowChrome>
 
     <Grid x:Name="MainGrid"
-          Background="{DynamicResource backgroundColor}">
+          Background="Transparent">
         <Border x:Name="MainWindowSurface"
                 CornerRadius="20"
                 BorderThickness="0"

MainWindow.xaml.cs

@@ -2172,25 +2172,27 @@ namespace C4IT_CustomerPanel
 
         private void UpdateMainSurfaceClip()
         {
-            if (MainWindowSurface == null)
+            if (MainWindowSurface == null || MainGrid == null)
                 return;
 
-            double width = MainWindowSurface.ActualWidth;
-            double height = MainWindowSurface.ActualHeight;
+            double width = MainGrid.ActualWidth;
+            double height = MainGrid.ActualHeight;
             if (width <= 0 || height <= 0)
                 return;
 
             const double outerRadius = 20d;
-            const double clipInset = 0.5d;
+            const double clipInset = 0d;
             double clipWidth = Math.Max(0d, width - (clipInset * 2d));
             double clipHeight = Math.Max(0d, height - (clipInset * 2d));
             double clipRadius = Math.Max(0d, outerRadius - clipInset);
-
-            MainWindowSurface.Clip = new RectangleGeometry(
+            RectangleGeometry clipGeometry = new RectangleGeometry(
                 new Rect(clipInset, clipInset, clipWidth, clipHeight),
                 clipRadius,
                 clipRadius);
 
+            MainGrid.Clip = clipGeometry;
+            MainWindowSurface.Clip = clipGeometry.Clone();
+
             _mainSurfaceClipInitialized = true;
         }