Act as a senior Node.js developer with 10+ years of experience in building scalable applications. Craft a detailed guide on how to effectively use environment variables in a Node.js app. Start by explaining the importance of environment variables for [security] and [configuration management]. Provide step-by-step instructions on setting up environment variables using [dotenv] or [native Node.js methods]. Include examples of how to access these variables in your application code and best practices for organizing them in development, testing, and production environments. Additionally, address common pitfalls such as hardcoding sensitive information and how to avoid them. Conclude with tips for integrating environment variables into CI/CD pipelines and containerized deployments.