ci(pages): deploy docs-site to GitHub Pages via Astro action

withastro/action@v3 (path=docs-site, bun) builds + uploads; actions/deploy-pages@v4
publishes. Triggers on push to main under docs-site/** (+ manual dispatch).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lidge-jun

.github/workflows/deploy-docs.yml

@@ -0,0 +1,45 @@
+name: Deploy Docs to GitHub Pages
+
+on:
+  # Rebuild when the docs site or this workflow changes on main.
+  push:
+    branches: [main]
+    paths:
+      - "docs-site/**"
+      - ".github/workflows/deploy-docs.yml"
+  # Allow manual runs from the Actions tab.
+  workflow_dispatch:
+
+# Least-privilege token needed to publish to GitHub Pages.
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Never run two Pages deploys at once; let an in-flight deploy finish.
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Build with Astro
+        uses: withastro/action@v3
+        with:
+          path: ./docs-site
+          package-manager: bun@latest
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4