sifatshams/whatsapp-clone ? reverse-engineered prompt

Build me a WhatsApp inspired real time messaging app with a simple clean chat interface.

I want a full stack app where people can sign up, log in, see a list of chats, open a conversation, and send messages instantly without refreshing. Make it feel like a modern messaging app, with a left side chat list and a main chat window on desktop, and a mobile friendly layout too.

Use the existing client and server setup and wire the whole thing together so messages are saved and loaded properly. If you need to look up current docs online for anything, do that. Please include basic user authentication, real time updates, and a polished but simple UI that feels close to WhatsApp. Keep the code organized and make sure it runs cleanly from the repo.