Fix Astro Pages Build job to resolve package manager in docs workspace

[Copilot]

The GitHub Actions Build job was failing because the Astro Pages workflow detected yarn.lock/package.json only at repo root, while the site lives under docs/. This updates workflow path resolution so dependency detection and build execution use the correct workspace.

• Workflow path configuration

  • Set BUILD_PATH to docs in .github/workflows/astro.yml so all build steps target the Astro project directory.

• Package manager detection fix

  • Updated detection checks to look in ${{ github.workspace }}/${{ env.BUILD_PATH }} instead of root.
  • This aligns manager detection with existing working-directory: ${{ env.BUILD_PATH }} usage in install/build steps.

• Relevant workflow change

  env:
    BUILD_PATH: "docs"
  
  if [ -f "${{ github.workspace }}/${{ env.BUILD_PATH }}/yarn.lock" ]; then
    ...
  elif [ -f "${{ github.workspace }}/${{ env.BUILD_PATH }}/package.json" ]; then
    ...
  fi