feat: add a dedicated now-playing display

[wizzomafizzo]

Add a dedicated display mode showing the game or core currently running on a connected Zaparoo device.

The intended use is a spare tablet, iPad, e-ink screen, or similar secondary display acting as a marquee. It could show the current title, artwork, playback status, and a small set of common controls in a fullscreen-friendly layout.

Source: https://discord.com/channels/1136235625486487622/1194050304484843651