The wallpaper autostart script was failing on Plasma 6 + Wayland,
causing the live session to show the default Plasma background instead
of the Antergos NeXT branded wallpaper.
Changes:
- Rewrote set-antergos-wallpaper.sh with three fallback methods:
1. plasma-apply-wallpaperimage (primary)
2. kwriteconfig6 + qdbus6 config reload
3. qdbus6 evaluateScript API
- Added direct wallpaper config in live-overlay/home/antergos/ for
the live user (most reliable, runs before Plasma starts)
- Updated existing /etc/skel/ and main.xml defaults to use
antergos-wallpaper.png instead of adwaita-morning.webp
- Downloaded and included original Antergos wallpaper from the
project's wallpapers repo