Update ThemeSelectorService to use ThemeListener

[LeftTwixWand]

Now the application toolbar is manually extended to match the Windows 11 style system.
But every time the theme has changed, we have to apply the toolbar style manually:

To avoid the code-behind, we can use the ThemeListener from the Community Toolkit to subscribe for the system theme change (if application theme is default) and handle it automatically in the separate service.