Builds the migration layer of a use case (UC-XXX) with Flyway: versioned V*.sql scripts with sequences, tables, snake_case columns, CHECK and UNIQUE constraints, and foreign keys from the entity model, placed in the migration location docs/architecture/stack.md records, and only the tables, columns, and constraints the use case needs that the schema does not have yet. Marks a constraint that enforces a business rule with -- UC-XXX BR-YYY. Normally run by /use-case-implement as the first layer; can be run directly, with a use case or for the whole entity model. Use when the user asks to "create a migration", "write a Flyway migration", "add a column", "create the tables for UC-001", "set up the database schema", or mentions Flyway, schema migration, DB migration, database versioning, or SQL migration files in a project that combines layer plugins. Test data migrations belong to the test skills.