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/packagechooser_de.conf

@@ -0,0 +1,128 @@
+---
+mode: required
+method: netinstall-add
+labels:
+    step: "Desktop Environment"
+default: Plasma
+items:
+    - id: Plasma
+      name: "KDE Plasma"
+      description: "Full-featured modern desktop. The default Antergos NeXT experience."
+      screenshot: ""
+      netinstall:
+        name: "KDE Plasma"
+        selected: true
+        critical: false
+        packages:
+          - plasma
+          - ark
+          - dolphin
+          - ffmpegthumbs
+          - gwenview
+          - kate
+          - keditbookmarks
+          - kfind
+          - kgpg
+          - kio-admin
+          - konsole
+          - konversation
+          - kwalletmanager
+          - okular
+          - partitionmanager
+          - antergos-next-desktop-settings
+    - id: Xfce
+      name: "Xfce"
+      description: "Lightweight traditional desktop. Fast and low on resources."
+      screenshot: ""
+      netinstall:
+        name: "Xfce"
+        selected: true
+        critical: false
+        packages:
+          - xfce4
+          - xfce4-goodies
+    - id: Cinnamon
+      name: "Cinnamon"
+      description: "Traditional desktop with modern features (GNOME-based)"
+      screenshot: ""
+      netinstall:
+        name: "Cinnamon"
+        selected: true
+        critical: false
+        packages:
+          - cinnamon
+          - cinnamon-control-center
+          - cinnamon-desktop
+          - cinnamon-menus
+          - cinnamon-screensaver
+          - cinnamon-session
+          - cinnamon-settings-daemon
+          - cinnamon-translations
+    - id: MATE
+      name: "MATE"
+      description: "Classic desktop — continuation of GNOME 2"
+      screenshot: ""
+      netinstall:
+        name: "MATE"
+        selected: true
+        critical: false
+        packages:
+          - mate
+          - mate-extra
+    - id: LXQt
+      name: "LXQt"
+      description: "Lightweight Qt-based desktop"
+      screenshot: ""
+      netinstall:
+        name: "LXQt"
+        selected: true
+        critical: false
+        packages:
+          - lxqt
+    - id: i3
+      name: "i3"
+      description: "Minimal tiling window manager (keyboard-driven)"
+      screenshot: ""
+      netinstall:
+        name: "i3"
+        selected: true
+        critical: false
+        packages:
+          - i3
+          - antergos-i3-config
+    - id: Sway
+      name: "Sway"
+      description: "i3-compatible Wayland compositor"
+      screenshot: ""
+      netinstall:
+        name: "Sway"
+        selected: true
+        critical: false
+        packages:
+          - sway
+          - swaybg
+          - swayidle
+          - swaylock
+          - antergos-sway-config
+    - id: Hyprland
+      name: "Hyprland"
+      description: "Dynamic tiling Wayland compositor with eye candy"
+      screenshot: ""
+      netinstall:
+        name: "Hyprland"
+        selected: true
+        critical: false
+        packages:
+          - hyprland
+          - xdg-desktop-portal-hyprland
+          - antergos-hyprland-config
+    - id: COSMIC
+      name: "COSMIC"
+      description: "Modern Rust-based desktop. Select greetd as DM."
+      screenshot: ""
+      netinstall:
+        name: "COSMIC"
+        selected: true
+        critical: false
+        packages:
+          - cosmic