ci: deploy to GitHub Pages on push to main

.github/workflows/deploy.yml

@@ -0,0 +1,39 @@
+# Builds dist/ and publishes it to GitHub Pages on every push to main.
+# Needs Settings → Pages → Source set to "GitHub Actions" once.
+name: Deploy
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# One deploy at a time; a newer push supersedes a running one.
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  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 run build
+      - uses: actions/configure-pages@v5
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: dist
+      - id: deployment
+        uses: actions/deploy-pages@v4