ci: add GitHub Pages deploy for remote manifest

.github/workflows/pages.yml

@@ -0,0 +1,41 @@
+name: Deploy site
+
+# Publishes the contents of site/ (the remote manifest that drives in-app
+# announcements + the update notice) to GitHub Pages.
+# One-time setup: Settings → Pages → Source: GitHub Actions.
+
+on:
+  push:
+    branches: [main]
+    paths: ["site/**", ".github/workflows/pages.yml"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow only one concurrent deployment; don't cancel an in-progress one.
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Upload site artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: site
+
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4