ci: add custom Pages deployment workflow

Replace legacy Jekyll-based Pages build with GitHub Actions workflow.
This gives us better control and reliability for deploying static content.

The workflow:
- Checks out gh-pages branch
- Uploads static files as Pages artifact
- Deploys to GitHub Pages

This bypasses the stuck legacy build system.

Author: longbinlai

.github/workflows/pages-deploy.yml

@@ -0,0 +1,39 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [gh-pages]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          ref: gh-pages
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: '.'
+
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4