Let OWE own video backgrounds while it runs

The background plugin now watches for the OWE daemon socket. While OWE is
running, the desktop yields video playback to it and the shell keeps
stills. The lock screen keeps its own playback.

This lets Omarchy cooperate with OWE without OWE editing shell.json, so
the engine can ship as a package.

Add a package-list note that owe-wallpaper-engine must be added once it is
packaged.

manual/39-backgrounds.md

@@ -4,6 +4,6 @@ Every theme ships with its own set of backgrounds, and you can add extras of you
 
 You can do this most easily by going to _Install > Style > Background_ in the Omarchy Menu. That'll bring up the folder where the backgrounds for that theme is stored. Hit `Super + Shift + F` to start another file manager, find your background, copy it over.  Now it'll be included in the choices of backgrounds you can select between using `Super + Ctrl + Space`.
 
-Backgrounds can be videos as well as stills. Drop an `mp4`, `m4v`, `mov`, `webm`, `mkv`, or `avi` file in the same folder and it appears alongside the images, playing on a loop. Only your first monitor's wallpaper plays a video's sound track, through the default audio output at the system volume, and the lock screen stays silent. Playback stops on its own whenever nothing can see it — while a fullscreen window covers that monitor, while the screensaver is up, and once a locked screen has gone dark — but a video wallpaper still costs far more power than a still one, and each monitor decodes its own copy.
+Backgrounds can be videos as well as stills. Drop an `mp4`, `m4v`, `mov`, `webm`, `mkv`, or `avi` file in the same folder and it appears alongside the images, playing on a loop. Only your first monitor's wallpaper plays a video's sound track, through the default audio output at the system volume, and the lock screen stays silent. Playback stops on its own whenever nothing can see it — while a fullscreen window covers that monitor, while the screensaver is up, and once a locked screen has gone dark — but a video wallpaper still costs far more power than a still one, and each monitor decodes its own copy. When the OWE wallpaper engine is running, it takes over video backgrounds and the shell keeps only stills.
 
 You can find a huge collection of cool curated backgrounds on https://github.com/dharmx/walls.