Rewrite with modern stack

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

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/config/database-factory.ts

@@ -0,0 +1,27 @@
+// Database factory that chooses between production and development database
+
+// Check if we should use development mode (no Redis/PostgreSQL available)
+const useDevelopmentMode = process.env.NODE_ENV === 'development' && 
+  (process.env.USE_MOCK_DB === 'true' || !process.env.REDIS_URL?.includes('://'));
+
+let redisClient: any;
+let pgPool: any;
+let initializeDatabase: () => Promise<void>;
+
+if (useDevelopmentMode) {
+  // Use development mock
+  const devDb = require('./database-dev');
+  redisClient = devDb.redisClient;
+  pgPool = devDb.pgPool;
+  initializeDatabase = devDb.initializeDatabase;
+  console.log('📦 Using development database (Mock)');
+} else {
+  // Use production database
+  const prodDb = require('./database');
+  redisClient = prodDb.redisClient;
+  pgPool = prodDb.pgPool;
+  initializeDatabase = prodDb.initializeDatabase;
+  console.log('🔥 Using production database');
+}
+
+export { redisClient, pgPool, initializeDatabase };