ci: add GitHub Actions workflow for Pages deployment

Author: Leftium

.github/workflows/pages.yml

@@ -0,0 +1,51 @@
+name: Deploy demo to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+
+      - run: npm ci
+
+      - run: node build.js
+
+      # Assemble _site so demo/../dist paths resolve correctly:
+      #   _site/demo/index.html  →  href="../dist/nimble.css"
+      #   _site/dist/nimble.css
+      - name: Assemble site
+        run: |
+          mkdir -p _site/demo _site/dist
+          cp demo/* _site/demo/
+          cp dist/* _site/dist/
+          # Redirect root to demo page
+          echo '<meta http-equiv="refresh" content="0;url=demo/">' > _site/index.html
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: _site
+
+      - id: deployment
+        uses: actions/deploy-pages@v4