Modernize collaborative pixel art platform to production-ready architecture

Major refactor from simple HTML/JS app to modern full-stack TypeScript application:

## Architecture Changes
- Migrated to monorepo structure with workspaces (backend, frontend, shared)
- Backend: Node.js + Express + TypeScript + Socket.IO
- Frontend: Next.js 15.5 + React 19 + TypeScript + Tailwind CSS
- Shared: Common types and utilities across packages

## Key Features Implemented
- Real-time WebSocket collaboration via Socket.IO
- Virtual canvas with chunked loading for performance
- Modern UI with dark mode and responsive design
- Mock database system for easy development (Redis/PostgreSQL compatible)
- Comprehensive error handling and rate limiting
- User presence and cursor tracking
- Infinite canvas support with zoom/pan controls

## Performance Optimizations
- Canvas virtualization - only renders visible viewport
- Chunked pixel data loading (64x64 pixel chunks)
- Optimized WebSocket protocol
- Memory-efficient state management with Zustand

## Development Experience
- Full TypeScript support across all packages
- Hot reload for both frontend and backend
- Docker support for production deployment
- Comprehensive linting and formatting
- Automated development server startup

## Fixed Issues
- Corrected start script paths
- Updated environment configuration
- Fixed ESLint configuration issues
- Ensured all dependencies are properly installed
- Verified build process works correctly

backend/.env.example

@@ -0,0 +1,30 @@
+# Server Configuration
+PORT=3001
+NODE_ENV=development
+CORS_ORIGIN=http://localhost:3000
+
+# Security
+JWT_SECRET=your-super-secret-jwt-key-change-in-production
+
+# Database Configuration
+REDIS_URL=redis://localhost:6379
+REDIS_KEY_PREFIX=gaplace:
+
+POSTGRES_HOST=localhost
+POSTGRES_PORT=5432
+POSTGRES_DB=gaplace
+POSTGRES_USER=gaplace
+POSTGRES_PASSWORD=password
+
+# Rate Limiting
+RATE_LIMIT_PIXELS_PER_MINUTE=60
+RATE_LIMIT_PIXELS_PER_HOUR=1000
+RATE_LIMIT_CURSOR_PER_SECOND=10
+
+# Canvas Configuration
+MAX_CANVAS_SIZE=10000
+DEFAULT_CANVAS_SIZE=1000
+CHUNK_SIZE=64
+
+# Logging
+LOG_LEVEL=info