New users get a one-time welcome window on first boot (self-gating marker,
skipped for the live/installer user) and a keybind cheatsheet on SUPER+/.
Also bind BOS Settings to SUPER+, (it had no launcher bind). Both popups
are floated/centred via window rules. Addresses the onboarding/
discoverability gap from external review.
The boot splash still used the old bread-brown background (#230b00)
after the rest of the theme moved to a black base (#0c0c0c). Switch
bos.script's background to black so the boot splash is consistent with
the wallpaper/pywal palette and breadbar.