Public Get Versions Flat

Get all versions/trims for a model (public, model-only).

The catalog cascade (/versions/{model_id}/{fuel_id}/{gearbox_id}) has no fuel/gearbox coverage for non-car sections (Comerciais/Motos/Pesados), so the website widget can't reach a version that way. This flat endpoint mirrors the protected /versions/{model_id} and returns the full version list straight off the model id.