Set initial video mode to muted to see if fixes audio takeover of background apps

lib/controls/audio_video/media_kit_av_control.dart

@@ -26,6 +26,7 @@ class _MediaKitAvControlState extends State<MediaKitAvControl> {
   final Player player = Player(
     configuration: const PlayerConfiguration(
       logLevel: MPVLogLevel.warn,
+      muted: true,
     ),
   );
   VideoController? controller;