feat: branding DE/DM selectors, slideshow content redesign, layan wallpaper fix

calamares-branding-antergos-next:
- Replace packagechooser.conf (method: legacy, init selector) with
  packagechooser_de.conf (9 DEs, netinstall-add) and packagechooser_dm.conf
  (5 DMs, netinstall-select)
- Clean netinstall.yaml: remove Budgie, split i3/Sway, drop hidden groups
- Update settings_online.conf with packagechooser@de + @dm instances
- Redesign slideshow: 7 slides, accurate copy (Artix-based, not Arch),
  accent bar, better layout
- Bump pkgrel to 23

antergos-layan-theme:
- Fix plasma-org.kde.plasma.desktop-appletsrc video wallpaper path:
  Retro%20Sun%20WPE.mp4 -> antergos-wallpaper.mp4

packages/antergos-layan-theme/Configs/Home/.config/plasma-org.kde.plasma.desktop-appletsrc

@@ -647,7 +647,7 @@ positions={"1920x1080":["1","17"],"2560x1440":[]}
 sortMode=-1
 
 [Containments][87][Wallpaper][luisbocanegra.smart.video.wallpaper.reborn][General]
-VideoUrls=["file:///usr/share/backgrounds/antergos/Retro%20Sun%20WPE.mp4"]
+VideoUrls=["file:///usr/share/backgrounds/antergos/antergos-wallpaper.mp4"]
 Volume=0
 MuteMode=5
 FillMode=2