Legal API - alteration to numbered company validation logic is incorrect

For alterations, there is currently [code](https://github.com/bcgov/lear/blob/a8ba290e4d267e558a8016286f4825036f9c3182/legal-api/src/legal_api/services/filings/validations/alteration.py#L119-L123) that validates the scenario where a named company is trying to altered to a numbered company. The validation logic just checks that the current business legal name has non-null value. This is incorrect as a numbered company will have a non-null value meaning that the validation does nothing.

Question: is this something we need to fix? It isn't actually a scenario that the FE currently handles.

Start with legal-api/src/legal_api/services/filings/validations/alteration.py at lines 119-123 and review how alterations distinguish named and numbered companies. Confirm whether the frontend is expected to support this scenario and what the validation should do. Done requires an agreed requirement and corresponding validation behavior, with coverage if the project identifies a relevant test location.

Written by the indexing model from the issue text.