Generate a FluentValidation validator for a .NET DTO or command — create,
update, delete, shared-save, or import variant — with rules grounded in the
DTO's real properties and the repo's existing validator conventions.
Uniqueness and dependency checks go through an adopter-owned abstraction, so
FluentValidation stays the only named third-party dependency. Use when asked
to write/generate/add a validator or "add validation for <DTO>".
