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

shared/package.json

@@ -0,0 +1,20 @@
+{
+  "name": "@gaplace/shared",
+  "version": "1.0.0",
+  "description": "Shared types and utilities for GaPlace",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "scripts": {
+    "build": "tsc",
+    "dev": "tsc --watch",
+    "clean": "rm -rf dist",
+    "type-check": "tsc --noEmit",
+    "lint": "eslint src --ext .ts,.tsx"
+  },
+  "devDependencies": {
+    "typescript": "^5.3.3"
+  },
+  "peerDependencies": {
+    "typescript": "^5.0.0"
+  }
+}