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/_config.yml

@@ -0,0 +1,28 @@
+title: Antergos NeXT
+description: >-
+  A community revival of Antergos — Artix Linux, OpenRC, KDE Plasma, Calamares
+theme: just-the-docs
+
+color_scheme: dark
+
+url: "https://antergos-next.github.io"
+baseurl: "/antergos-iso"
+
+aux_links:
+  "Antergos NeXT on GitHub":
+    - "https://github.com/Antergos-NeXT/antergos-iso"
+aux_links_new_tab: true
+
+heading_anchors: true
+search_enabled: true
+search:
+  heading_level: 3
+  previews: 3
+
+back_to_top: true
+back_to_top_text: "Back to top"
+
+footer_content: "Copyright &copy; Antergos NeXT contributors. Distributed under the <a href=\"https://github.com/Antergos-NeXT/antergos-iso/blob/master/LICENSE\">GPL-3.0 License.</a>"
+
+plugins:
+  - jekyll-seo-tag