Add comprehensive Docker support for easy deployment

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This PR adds complete Docker support to enable easy deployment of the Minecraft reverse proxy service in containerized environments.

What's Added

🐳 Multi-stage Dockerfile

• Optimized production image (134MB) using Alpine Linux base
• Security-focused with non-root user (minecraft:nodejs)
• Built-in health checks for container monitoring
• Support for environment variables (VERBOSE_LEVEL, NODE_ENV)

🚀 Docker Compose Setup

• docker-compose.yml for production deployment
• docker-compose.dev.yml override for development with verbose logging
• Resource limits and logging configuration
• Single-command deployment: docker compose up -d

📦 npm Scripts
Added convenient Docker commands to package.json:

npm run docker:build     # Build Docker image
npm run compose:up       # Start with Docker Compose
npm run compose:down     # Stop containers
npm run compose:logs     # View logs
npm run compose:dev      # Development mode with verbose logging

📚 Documentation

• Updated README with comprehensive Docker usage instructions
• Created DOCKER.md with advanced examples and configuration
• Added config.docker-example.json for container network setups

Key Features

• Environment Configuration: VERBOSE_LEVEL environment variable support
• Security: Non-root container execution with proper file permissions
• Health Monitoring: Built-in health checks using netcat
• Development Support: Development compose override for debugging
• Resource Management: Memory and CPU limits configuration
• Easy Deployment: Single-command setup for production use

Usage

# Quick start
cp config-example.json config.json
# Edit config.json for your servers
docker compose up -d

The implementation maintains full compatibility with existing functionality including Proxy Protocol support for preserving client IPs through load balancers.

Fixes #2.

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