Adds Counter, Timestamp, Uuid (canonical and compact), and Random (base32/base36) namers, each documenting its pool size and what it leaks (an ordinal, a mint time, nothing). check() now delegates to didbot_identity::validate_label instead of a hand-rolled copy. Namer gains max_useful_attempts so a single-shot generator like Counter is asked once instead of retried through the 16-attempt loop it can never satisfy differently. plan/zone-scale.md's pool-size table and checklist item are updated to match. Change-Id: I91c126eb8e8a973f3ecdfd2a2e2cb6903cfe0ac4