Real-time Chat

# Real-time Chat PRD

## Overview
Build a real-time chat application supporting multiple rooms.

## Requirements
- WebSocket-based real-time messaging
- Multiple chat rooms (create, join, leave)
- Message history (last 100 messages per room)
- Username selection on join
- Online user list per room
- Message timestamps
- Auto-scroll to latest message

## Tech Stack
- Node.js backend with WebSocket (ws or socket.io)
- Any frontend framework
- In-memory storage (no database required)

## Scoring Criteria
- **Functional (40%)**: Real-time messaging works, rooms work, history loads
- **Quality (20%)**: Clean architecture, error handling, no memory leaks
- **Fidelity (25%)**: All described features present and working
- **Speed (15%)**: Time bonus