Flyway V70: SMALLINT generation column with CHECK(0..10) and partial
index over non-null rows. Person.generation field surfaces it through
the JPA model. Pre-import rows and persons outside the curated family
graph legitimately stay null; the canonical importer (next commits)
back-fills via preferHuman so a human-edited value is never lost.
Refs #689
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>