Crazy idea, but maybe change the rules of Show HN so that you are required to include in the headline how long you have been working on the project. As an example, something like:

Show HN: My Project - A description for my vibe coded project [3 weeks]

A lot of the good stuff I see on Show HN are projects that have been worked on for a long time. While I understand that vibe coding is newer trend, I also know that vibe coded projects are less likely to stand the test of time. With this, we don't have to worry about whether a project is AI assisted or not, nor do we ban it. Instead just incentivize longer term projects. If the developer lies about how long they worked on the project, they will get reported and downvoted into oblivion.