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/

.github/workflows/build.yml

@@ -70,7 +70,7 @@ jobs:
         path: ${{ github.workspace }}/iso/
 
     - name: Upload to Internet Archive
-      if: github.ref == 'refs/heads/master'
+      if: false  # temporarily disabled until ISO is stable
       env:
         IA_ACCESS_KEY: ${{ secrets.IA_ACCESS_KEY }}
         IA_SECRET_KEY: ${{ secrets.IA_SECRET_KEY }}

.github/workflows/pages.yml

@@ -0,0 +1,55 @@
+name: Deploy docs to Pages
+
+on:
+  push:
+    branches: ["master"]
+    paths: ["docs/**"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: docs
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+          bundler-cache: true
+          cache-version: 0
+          working-directory: '${{ github.workspace }}/docs'
+      - name: Setup Pages
+        id: pages
+        uses: actions/configure-pages@v6
+      - name: Build with Jekyll
+        run: bundle exec jekyll build --baseurl "${{ steps.pages.outputs.base_path }}"
+        env:
+          JEKYLL_ENV: production
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v4
+        with:
+          path: docs/_site/
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v5