I would trust an LLM with backend much more than front-end. Especially if we're talking monolithic and good type system. Ideally compiled. When I say trust I mean it's not going to break the user-facing API contract, probably, even if internally it's a mess. If you let it do front-end blind, it will almost certainly embarrass you if you care at all about user experience.
If you do backend blind, it will also almost certainly embarrass you. I’ve never had an experience beyond the most basic crud app where I didn’t have to somehow use my engineering experience to dig it out of a hole.