Adjust the corner radius of the icons pane & enhance grid transition in IconographyPage (#1901)

## Screenshots (if appropriate):
**Before**

![image](https://github.com/user-attachments/assets/02f3a408-efa0-4bd0-8013-ef7a32d97c44)
**After**

![image](https://github.com/user-attachments/assets/8ece055e-87f1-4cc6-bbe3-35b75ca7abbe)
![Enregistrement 2025-06-12
171025](https://github.com/user-attachments/assets/8ba3a43e-b816-46dd-a478-700bb3a4478e)
## Types of changes
<!--- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

Author: Zakariathr22

WinUIGallery/Samples/ControlPages/Design/IconographyPage.xaml

@@ -89,6 +89,9 @@
     </Page.Resources>
 
     <Grid RowSpacing="8">
+        <Grid.ChildrenTransitions>
+            <RepositionThemeTransition/>
+        </Grid.ChildrenTransitions>
         <Grid.RowDefinitions>
             <RowDefinition Height="Auto" />
             <RowDefinition Height="Auto" />
@@ -185,6 +188,7 @@
                     BorderBrush="{ThemeResource DividerStrokeColorDefaultBrush}"
                     BorderThickness="1,0,0,0"
                     DataContext="{x:Bind}"
+                    CornerRadius="0,8,8,0"
                     Visibility="Collapsed">
                     <ScrollViewer>
                         <StackPanel Margin="16,16,8,16" Spacing="2">