Commit 76cbdaa3 destroyed the YAML indentation of NAYY, NAYCWY, NAY2Y,
NA2XY and NA2X2Y, silently dropping them from the catalog (404 detail
pages, missing from category listing and sitemap). Restored the valid
frontmatter from 76cbdaa3~1 (whitespace-only diff, content unchanged)
and added a content contract spec guarding parseability and catalog
visibility.
