photoframe: Start photo slide show on idle

The `photoframe` script was based on the one used by the original
Buildroot-based photo frame system.  I've split it into two processes,
though: one to listen to the URL stream and download new photos as
instructed by the server, and another to actually display the photos.
Getting `feh` and Firefox to both be fullscreen at the same time was
difficult, and only works if they are on separate Sway workspaces. Thus,
"activating" the slide show means switching to the workspace where `feh`
is and "deactivating" it means switching back to Firefox's workspace.

install.packages

@@ -1,3 +1,6 @@
+gui-apps/swayidle
 gui-wm/sway
-net-wireless/wpa_supplicant
+media-gfx/feh
 media-video/pipewire
+net-misc/curl
+net-wireless/wpa_supplicant