PersonService and RelationshipService each carried a verbatim copy of the
date⇔precision coherence check and the null→UNKNOWN precision normalizer.
Hoist both into a single document.DatePrecisionValidation util so the rule
that the V76/V78 CHECK constraints mirror has one source of truth. Each
service keeps its own order check (BIRTH_AFTER_DEATH vs
INVALID_RELATIONSHIP_DATES), which is the only genuinely domain-specific part.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>