Fix GitHub Pages deployment permissions

Add required permissions to deploy job for OIDC authentication. The
actions/deploy-pages@v4 action needs pages:write and id-token:write
permissions to successfully deploy to GitHub Pages.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.github/workflows/main.yml

@@ -28,6 +28,9 @@ jobs:
     if: github.event_name == 'push' && github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
     needs: build
+    permissions:
+      pages: write
+      id-token: write
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}