openai/gpt-chat-latest → A (9:2)

Side A restores substantial web UI functionality by adding browser session cookies, login/logout flows, authenticated web posting, room-aware routing and permissions, private room pages, and reusable thread/navigation abstractions wired into the router. Side B is a focused UX improvement that changes the username form to return HTML fragments and updates the client-side form handler to morph form contents instead of redirecting, plus minor CSS additions.