Notifications on track change

[NattyNarwhal]

Apple Music and Cog do this. Should be optional - or is just suppressing notifications sufficient UX?

[NattyNarwhal]

See:

• https://developer.apple.com/documentation/usernotifications - use this instead of the one deprecated in Big Sur
• https://cocoacasts.com/local-notifications-with-the-user-notifications-framework

[NattyNarwhal]

Implemented, though...

• would be nice to have UI other than "lol change it in System Prefs" if we do more
• a skip button would be cool but inessential
• we always post the notification, which means we do get a notification always - but the default behaviour is to suppress it in the foreground
• other possibilities - there's no more chat, but other people's now playing might be cool?