Add Office 2016 support, bump to v1.20

Office 2016 Standard, Professional Plus, and Home & Business editions
added with PerpetualVL2019 channel for volume licenses.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

MainWindow.xaml

@@ -45,7 +45,7 @@
                                    Foreground="{StaticResource TextSecondaryBrush}" Margin="0,-2,0,0"/>
                     </StackPanel>
                 </StackPanel>
-                <TextBlock Text="v1.19" HorizontalAlignment="Right" VerticalAlignment="Center"
+                <TextBlock Text="v1.20" HorizontalAlignment="Right" VerticalAlignment="Center"
                            FontSize="12" Foreground="{StaticResource TextSecondaryBrush}"/>
             </Grid>
         </Border>