feat: add GitHub Pages docs site (Just the Docs), split packagechooser, disable IA upload

- docs/: new 13-page Jekyll site with Just the Docs theme
  - Home, Building, Installer, Packages, CI/CD, Development
  - Desktop Environments (with GNOME joke), Wallpapers, Launcher
  - Overlays, Root Overlay, Live Overlay
- .github/workflows/pages.yml: build & deploy docs from docs/ on
  push to master (only when docs/ changes)
- .github/workflows/build.yml: temporarily disable Internet Archive
  upload (if: false) until ISO is stable
- live-overlay/settings.conf: add instances section for init + desktop
  packagechooser instances
- live-overlay/modules/packagechooser_init.conf: init system selector
  (OpenRC, Runit, S6, Dinit) via netinstall-add method
- live-overlay/modules/packagechooser_desktop.conf: DE selector
  (Plasma, Xfce, Cinnamon, MATE, LXQt, i3, Sway, Hyprland + No Desktop)
  via legacy method
- README.md, AGENTS.md: fix sudo buildiso -> sudo ./buildiso, add note
  about system buildiso lacking --overwrite='*'
- .gitignore: add docs/_site/

docs/overlay-root.md

@@ -0,0 +1,51 @@
+---
+title: Root Overlay
+layout: default
+parent: Overlays
+nav_order: 1
+---
+
+# Root Overlay
+
+Files in `iso-profiles/antergos/root-overlay/` are merged into the root squashfs and become part of the installed system.
+
+## Contents
+
+```
+root-overlay/
+├── etc/
+│   ├── os-release            # Antergos NeXT branding
+│   ├── pacman.conf           # Includes [antergos-pkgs] repo
+│   ├── sddm.conf.d/
+│   │   └── kde_settings.conf # SDDM theme + Wayland session
+│   └── skel/
+│       └── .config/
+│           └── autostart/
+│               └── antergos-wallpaper.desktop  # One-shot wallpaper setter
+└── usr/
+    └── local/
+        └── bin/
+            └── set-antergos-wallpaper.sh  # Wallpaper script
+```
+
+## Key files
+
+### `etc/os-release`
+
+Identifies the system as "Antergos NeXT" to tools, installers, and the login manager.
+
+### `etc/pacman.conf`
+
+Adds the `[antergos-pkgs]` custom repo so installed systems can receive updates.
+
+### `etc/sddm.conf.d/kde_settings.conf`
+
+Sets the SDDM session to `plasma.desktop` (Wayland) by default.
+
+### `etc/skel/.config/autostart/antergos-wallpaper.desktop`
+
+Runs the wallpaper setter on first login. Uses `X-KDE-autostart-phase=2` to run after Plasma has initialized.
+
+### `usr/local/bin/set-antergos-wallpaper.sh`
+
+Applies the wallpaper via `plasma-apply-wallpaperimage` and creates `~/.config/antergos-wallpaper-set` marker to prevent re-running.