Add is_identifier_registrar so only the production instance may mint
hub UUIDs into repository files. Workstation hubs stay read/project
caches until deterministic derivation lands.
Also close RMGR-WP-0004-T05: register cutover is STATE-WP-0080-T02.
Implement RMGR-WP-0004 T01 (flavor, required files, anti-patterns from
canon) and T08 (prefix ownership registry plus uniqueness scan).
rmgr conform and rmgr prefix-uniqueness are detection only.
