chore(ci): add GitHub Pages build and deploy workflow

.github/workflows/deploy-pages.yml

@@ -0,0 +1,53 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+# Allow the deploy job to publish to Pages via OIDC.
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Only one Pages deployment at a time; cancel superseded runs.
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+
+      # base must match the project-page path: https://<owner>.github.io/macroplan/
+      - run: pnpm build
+
+      - uses: actions/configure-pages@v5
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: dist
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - id: deployment
+        uses: actions/deploy-pages@v4