Fix Build site workflows to use Quarto project subdirectory output

[Copilot]

The Build site job failed because workflow steps assumed _site exists at repository root, while the Quarto project lives in librosa_blog/ and renders output there. This updates CI/deploy workflows to run from the correct directory and upload the actual rendered path.

• Root cause

  • Workflows rendered from repo root but Quarto config is under librosa_blog/.
  • Pages artifact upload targeted _site instead of librosa_blog/_site.

• Workflow updates

  • CI (.github/workflows/ci.yml)
    • Run quarto render with working-directory: librosa_blog.
  • Deploy (.github/workflows/deploy.yml)
    • Run quarto render with working-directory: librosa_blog.
    • Upload artifact from librosa_blog/_site.

• Illustrative change

  - name: Render site
    working-directory: librosa_blog
    run: quarto render
  
  - name: Upload Pages artifact
    uses: actions/upload-pages-artifact@v3
    with:
      path: librosa_blog/_site