Run as a separate command-line app

[mkozjak]

Reuse existing OSD to be able to show it using a small command-line program without running Volume-Control.

My use-case for this is to have a global hotkey that I use to run a Shortcut that contacts with the Hi-Fi appliance to modify its volume and return the current value. I would then use this value to feed it to volume-control cli (I used showosd until Tahoe) to draw myself an OSD with current Hi-Fi volume on my screen.