ci: add GitHub Actions workflow to deploy to GitHub Pages

Add deploy.yml workflow that runs tests, builds, and deploys to
GitHub Pages on push to main. Add vite.config.js with base path
for subdirectory hosting. Include deployment spec.

.github/workflows/deploy.yml

@@ -0,0 +1,44 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - run: npm ci
+
+      - run: npm test
+
+      - run: npm run build
+
+      - uses: actions/configure-pages@v5
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: dist
+
+      - id: deployment
+        uses: actions/deploy-pages@v4