Change bundle-manifest discovery from bundles/*/manifest.yaml to */manifest.yaml
and rebuild the tmpdir fixtures in test-validate-bundles.rb at the tmpdir root
so manifests live at <skill>/manifest.yaml and path fields use the flattened
relative depth. Refresh the validator's header comment.
Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>