Migrate to native GitHub Pages deployment (no gh-pages branch) (#499)

* Migrate to native GitHub Pages deployment (no gh-pages branch)

- Replace peaceiris/actions-gh-pages@v4 with native actions/deploy-pages@v4
- Add required permissions (pages: write, id-token: write) and environment
- Add concurrency group to prevent deployment conflicts
- Update linkcheck.yml to download Pages artifact instead of checking out gh-pages
- Enables future deletion of gh-pages branch to reclaim ~300MB repo space

Closes #419

* Address Copilot review: add actions:read permission, use release assets for linkcheck

- Add actions: read permission to publish.yml (needed by dawidd6/action-download-artifact)
- Switch linkcheck.yml from expiring Pages artifact to permanent release asset (tar.gz)
- Eliminates dependency on artifact retention window for link checking

Author: mmcky

.github/workflows/linkcheck.yml

@@ -11,15 +11,23 @@ jobs:
     permissions:
       issues: write   # required for QuantEcon link-checker
     steps:
-      # Checkout the live site (html)
-      - name: Checkout
-        uses: actions/checkout@v6
-        with:
-          ref: gh-pages
+      # Download the latest release HTML archive (permanent, not subject to artifact expiry)
+      - name: Get latest release asset URL
+        id: release
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          ASSET_URL=$(gh api repos/${{ github.repository }}/releases/latest \
+            --jq '.assets[] | select(.name | endswith(".tar.gz")) | .browser_download_url')
+          echo "asset-url=$ASSET_URL" >> $GITHUB_OUTPUT
+      - name: Download and extract release HTML
+        run: |
+          mkdir -p _site
+          curl -sL "${{ steps.release.outputs.asset-url }}" | tar -xz -C _site
       - name: AI-Powered Link Checker
         uses: QuantEcon/action-link-checker@main
         with:
-          html-path: '.'            # gh-pages live html
+          html-path: '_site'
           fail-on-broken: 'false'
           silent-codes: '403,503'
           ai-suggestions: 'true'

.github/workflows/publish.yml

@@ -3,10 +3,24 @@ on:
   push:
     tags:
       - 'publish*'
+
+permissions:
+  contents: write
+  actions: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
 jobs:
   publish:
     if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags')
     runs-on: "runs-on=${{ github.run_id }}/family=g4dn.2xlarge/image=quantecon_ubuntu2404/disk=large"
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - name: Checkout
         uses: actions/checkout@v6
@@ -113,12 +127,17 @@ jobs:
             html-manifest.json
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-      - name: Deploy website to gh-pages
-        uses: peaceiris/actions-gh-pages@v4
+      - name: Add CNAME for custom domain
+        run: echo "python-programming.quantecon.org" > _build/html/CNAME
+      - name: Setup Pages
+        uses: actions/configure-pages@v5
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
         with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: _build/html/
-          cname: python-programming.quantecon.org
+          path: _build/html/
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4
       - name: Prepare lecture-python-programming.notebooks sync
         shell: bash -l {0}
         run: |