Fix GitHub Pages deploy failure by replacing subtree force-push flow

[Copilot]

The deploy job in the GitHub Pages workflow was failing during git subtree push with remote commit_refs rejection. This change replaces the fragile subtree-based publish path with a direct gh-pages branch update flow.

• Root issue addressed

  • Removed the git subtree split + force-push pattern that produced remote rejection on tmp -> gh-pages.

• Deployment flow changes (.github/workflows/github-pages.yml)

  • Preserve generated site output in /tmp/deploy_temp.
  • Resolve gh-pages deterministically:
    • checkout remote gh-pages if it exists
    • otherwise initialize an orphan gh-pages branch
  • Replace branch contents with current build artifacts.
  • Commit only when there is an actual diff.
  • Push gh-pages directly (no subtree branch, no force push).

• Behavioral impact

  • Deployment remains artifact-driven and idempotent.
  • No-op deployments now exit cleanly without creating empty commits.

- name: Deploy to GitHub Pages
  run: |
    mv deploy_temp /tmp/deploy_temp
    if git ls-remote --exit-code --heads origin gh-pages >/dev/null 2>&1; then
      git fetch origin gh-pages
      git checkout -B gh-pages origin/gh-pages
    else
      git checkout --orphan gh-pages
      git rm -rf . || true
    fi
    find . -mindepth 1 -maxdepth 1 ! -name .git -exec rm -rf {} +
    cp -a /tmp/deploy_temp/. .
    git add -A
    if git diff --cached --quiet; then exit 0; fi
    git commit -m "$PDFRX_VERSION $GITHUB_SHA"
    git push origin gh-pages