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/calamares-branding-antergos-next/settings_online.conf

@@ -6,7 +6,8 @@ sequence:
         - welcome
         - locale
         - keyboard
-        - packagechooser
+        - packagechooser@de
+        - packagechooser@dm
         - netinstall
         - partition
         - users
@@ -37,6 +38,14 @@ sequence:
     - show:
         - finished
 
+instances:
+- id:       de
+  module:   packagechooser
+  config:   packagechooser_de.conf
+- id:       dm
+  module:   packagechooser
+  config:   packagechooser_dm.conf
+
 branding: antergos-next
 
 prompt-install: false