Add open-notch music visibility modes

[pr28416]

Summary

• Add a new media setting that controls when the open-notch music player is shown.
• Add three modes: Always, Only when music is playing, and Never.
• Update NotchHomeView to render the music player according to the selected mode.

Settings UI

• Replace the single on/off behavior with a picker under Media controls.
• Disable music slot and lyrics controls when mode is set to Never.

Issue

Closes #1025