Board game night scheduler, ChatGPT put the whole backend in one file

Unsure about: Structure

Weekly game night for about 30 people. ChatGPT wrote the Express backend and all of it lives in server.js, roughly 900 lines: sessions, RSVP logic, the reminder mail, the admin routes. It works and I can still find things. Before I add a second group I'd like to know whether splitting it is worth the churn, and where the natural seams are.