TimestampMixin (byte-identical to the hand-written pair — zero schema
migrations) adopted by 52 classes across 44 model files; the utcnow
tz-aware migration is now a one-file edit. uuid_pk() replaces the 13
pasted String(36) uuid4 lambdas across 7 files (ai.py's hex variant
stays grandfathered, documented). Deviant shapes (indexed created_at,
sanitization_profile's default-less updated_at, created-only models)
deliberately keep their own columns.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
