The migration spec only asserted SQL substrings against a mocked
QueryRunner and had no getMetadataArgsStorage() check that ShopOffer's
column options and partial unique indexes actually match the new
schema. Since ts-jest does not type-check in this package
(isolatedModules: true), this is the only automated guard against
entity/migration drift -- matches the house convention in
npc-system.migration.spec.ts and loot-bags.migration.spec.ts.