Add About dialog with version info

- About button added next to Exit in header
- Shows app name, version, author, and company
- Version 1.1.4

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

DellMonitorControl/MainWindow.xaml

@@ -188,8 +188,12 @@
             <Border Grid.Row="0" Background="#444" CornerRadius="8,8,0,0" Padding="12,10">
                 <Grid>
                     <TextBlock Text="Monitor Control" Foreground="White" FontSize="14" FontWeight="SemiBold" VerticalAlignment="Center"/>
-                    <Button Content="Exit" HorizontalAlignment="Right" Click="ExitButton_Click"
-                            Style="{StaticResource DarkButton}" FontSize="11"/>
+                    <StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
+                        <Button Content="About" Margin="0,0,6,0" Click="AboutButton_Click"
+                                Style="{StaticResource DarkButton}" FontSize="11"/>
+                        <Button Content="Exit" Click="ExitButton_Click"
+                                Style="{StaticResource DarkButton}" FontSize="11"/>
+                    </StackPanel>
                 </Grid>
             </Border>