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

docker-compose.yml

@@ -0,0 +1,76 @@
+version: '3.8'
+
+services:
+  redis:
+    image: redis:7-alpine
+    ports:
+      - "6379:6379"
+    volumes:
+      - redis_data:/data
+    command: redis-server --appendonly yes
+    healthcheck:
+      test: ["CMD", "redis-cli", "ping"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+
+  postgres:
+    image: postgres:15-alpine
+    environment:
+      POSTGRES_DB: gaplace
+      POSTGRES_USER: gaplace
+      POSTGRES_PASSWORD: password
+    ports:
+      - "5432:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U gaplace"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+
+  backend:
+    build:
+      context: .
+      dockerfile: backend/Dockerfile
+    ports:
+      - "3001:3001"
+    environment:
+      - NODE_ENV=development
+      - REDIS_URL=redis://redis:6379
+      - POSTGRES_HOST=postgres
+      - POSTGRES_PORT=5432
+      - POSTGRES_DB=gaplace
+      - POSTGRES_USER=gaplace
+      - POSTGRES_PASSWORD=password
+      - JWT_SECRET=development-secret-change-in-production
+    depends_on:
+      redis:
+        condition: service_healthy
+      postgres:
+        condition: service_healthy
+    volumes:
+      - ./backend:/app
+      - /app/node_modules
+    command: npm run dev
+
+  frontend:
+    build:
+      context: .
+      dockerfile: frontend/Dockerfile
+    ports:
+      - "3000:3000"
+    environment:
+      - NEXT_PUBLIC_BACKEND_URL=http://localhost:3001
+    depends_on:
+      - backend
+    volumes:
+      - ./frontend:/app
+      - /app/node_modules
+      - /app/.next
+    command: npm run dev
+
+volumes:
+  redis_data:
+  postgres_data: