#1718 Show a clock in the closed notch on displays without a notch

On displays without a physical notch the closed notch is an empty pill while nothing is playing, and while music plays the part a notch would cover stays empty. This adds an option under Settings > Appearance > Idle state to show the time there, optionally with the date. It follows the system 12/24-hour and date format. Off by default.

The clock shows in the closed notch when idle and between the album art and the visualizer while music plays. Notifications cover it, and with the face animation on, the face takes its place while idle. Notched displays are unchanged.

Idle	While music plays

Tested on macOS 27.0.1 with an external display. Unit tests pass.