Improve focus handling and window initialization

Added `IsTabStop="True"` to `RootGrid` in `MainWindow.xaml` to make it focusable. Updated `DispatcherQueue.TryEnqueue` in `MainWindow.xaml.cs` to clear focus from interactive elements (e.g., sliders) on window open, preventing unwanted tooltips and ensuring a cleaner initial state.

src/modules/powerdisplay/PowerDisplay/PowerDisplayXAML/MainWindow.xaml

@@ -21,7 +21,7 @@
         <DesktopAcrylicBackdrop />
     </winuiex:WindowEx.SystemBackdrop>
 
-    <Grid x:Name="RootGrid">
+    <Grid x:Name="RootGrid" IsTabStop="True">
         <Grid.Resources>
             <Style
                 x:Key="FlyoutButtonStyle"

src/modules/powerdisplay/PowerDisplay/PowerDisplayXAML/MainWindow.xaml.cs

@@ -219,7 +219,14 @@ namespace PowerDisplay
                 // This is critical because the OS might restore the window to a previous (incorrect) size
                 // when ShowWindow is called, ignoring our pre-show adjustment.
                 // By queuing this on the dispatcher, we ensure it runs after the window is visible and layout is active.
-                DispatcherQueue.TryEnqueue(() => AdjustWindowSizeToContent());
+                DispatcherQueue.TryEnqueue(() =>
+                {
+                    AdjustWindowSizeToContent();
+
+                    // Clear focus from any interactive element (e.g., Slider) to prevent
+                    // showing the value tooltip when the window opens
+                    RootGrid.Focus(FocusState.Programmatic);
+                });
 
                 bool isVisible = IsWindowVisible();
                 if (!isVisible)