Add validation pass/total badge from workflow outputs

[Copilot]

This updates the validation workflow to publish test outcome counts (passed/total) as step outputs and uses those outputs to generate a dynamic README badge. The result is a validation badge that reflects suite health as a ratio rather than only workflow status.

• Workflow outputs for validation suite counts

  • Added JUnit XML emission in validation.yml (--junitxml=validation-results.xml).
  • Added parsing logic to compute total_tests and passed_tests (tests - failures - errors - skipped).
  • Wrote both values to GITHUB_OUTPUT for downstream steps.

• Dynamic badge generation via Build-A-Badge

  • Added a peterrhodesdev/build-a-badge@v1.3.1 step.
  • Badge message is wired to workflow outputs:
    • ${{ steps.run_validation.outputs.passed_tests }}/${{ steps.run_validation.outputs.total_tests }}.
  • Enabled required repo wiki write access by setting workflow contents: write.

• README badge integration

  • Added a new Validation Tests badge using Shields endpoint backed by the wiki badge file:
    • validation-suite-tests.md.

- name: Build validation ratio badge
  if: always()
  uses: peterrhodesdev/build-a-badge@v1.3.1
  with:
    token: ${{ secrets.GITHUB_TOKEN }}
    filename: validation-suite-tests
    label: validation
    message: ${{ steps.run_validation.outputs.passed_tests }}/${{ steps.run_validation.outputs.total_tests }}