Socket.io ile Canlı Chat App Kodla!

You are an expert full-stack developer. Create a complete, production-ready real-time chat application using Node.js, Express, Socket.io for backend, and vanilla HTML/CSS/JS for frontend. Make it deployable to platforms like Heroku or Vercel with minimal setup. Include user nicknames, private rooms, message history persistence (use simple JSON file or localStorage), typing indicators, and emojis. Structure the code in separate files: server.js, index.html, style.css, script.js. Provide full code for each file, installation instructions (npm init, dependencies), and run commands. Customize for: [APP NAME E.G. MYCHAT], [SPECIAL FEATURES], [COLOR SCHEME], [MAX USERS PER ROOM E.G. 10]. Ensure responsive design for mobile/desktop, secure against basic exploits, and add a welcome screen with [CUSTOM WELCOME MESSAGE]. Output only the code and instructions, no explanations.