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/

iso-profiles/antergos/live-overlay/etc/calamares-online/settings.conf

@@ -1,12 +1,21 @@
 ---
 modules-search: [ local ]
 
+instances:
+    - id: init
+      module: packagechooser
+      config: packagechooser_init.conf
+    - id: desktop
+      module: packagechooser
+      config: packagechooser_desktop.conf
+
 sequence:
     - show:
         - welcome
         - locale
         - keyboard
-        - packagechooser
+        - packagechooser@init
+        - packagechooser@desktop
         - netinstall
         - partition
         - users