ci: add GitHub Actions workflow for GitHub Pages deployment

.github/workflows/deploy.yml

@@ -0,0 +1,70 @@
+# Deploy Music Blocks to GitHub Pages
+#
+# Prerequisite (one-time): A repo admin must set the Pages source to
+# "GitHub Actions" under Settings > Pages > Build and deployment.
+#
+# Triggers on every push to master and via manual workflow_dispatch.
+# Runs Jest tests first; deploys only if tests pass.
+
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [master]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  test:
+    name: Run Tests
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run Jest tests
+        run: npm test
+
+  deploy:
+    name: Deploy
+    needs: test
+    if: github.repository == 'sugarlabs/musicblocks'
+    runs-on: ubuntu-latest
+
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Configure Pages
+        uses: actions/configure-pages@v5
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: '.'
+
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4