Add GitHub Actions workflow to build and deploy to gh-pages

Builds the Vite app on push to main and publishes dist/ to the
gh-pages branch, so the live site updates automatically on merge.

https://claude.ai/code/session_01DUbsS9TjUPnaAbLQTnyczE

Author: claude

.github/workflows/deploy.yml

@@ -0,0 +1,43 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [ main ]
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+concurrency:
+  group: pages-deploy
+  cancel-in-progress: true
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 18
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Build
+        run: npm run build
+
+      - name: Copy static files into dist
+        run: |
+          cp robots.txt dist/robots.txt
+          cp manifest.json dist/manifest.json
+
+      - name: Deploy to gh-pages
+        uses: peaceiris/actions-gh-pages@v4
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./dist
+          publish_branch: gh-pages