initialize() now delegates to _apply_schema(): real boots run
'alembic upgrade head' (schema owned by the migration history); tests
(DECNET_TESTING=1) keep create_all, which is faster and needs no upgrade
path. MySQL wraps the upgrade in the existing GET_LOCK advisory lock so
concurrent uvicorn workers don't race on DDL.
Deletes the three _migrate_* crimes (attackers-table legacy drop +
GeoIP backfill, TEXT->MEDIUMTEXT widening) — all now handled by the
baseline migration and the _BIG_TEXT model variants. Drops the test
file that only exercised the deleted helpers; adds tests pinning the
alembic-vs-create_all gate and guarding that every model table is in
the migration head.