Enhances the parallel_beads workflow to capture and report validation status:
- Add step 3 to extract validation criteria from plans or use best-effort
fallbacks (make test, nix flake check, npm test)
- Update step 4 to run validation and track PASS/FAIL/SKIP results
- Add Validation section with table to PR body templates (gh and tea)
- Enhance result reporting to include validation summary
- Add Validation column and Validation Failures section to summary table
Implements bead: nixos-configs-39m
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>