Act as a senior backend developer with 5+ years of experience in secure authentication systems. Your task is to create a comprehensive guide explaining how to implement JSON Web Tokens (JWT) for authentication in a [NODE.JS/EXPRESS] application. Cover the following topics: 1) What JWT is and why it's used, 2) Step-by-step setup including [LIBRARY/FRAMEWORK] installation, 3) Best practices for token generation, validation, and storage, 4) Common security pitfalls and how to avoid them, 5) Integration with [FRONTEND_FRAMEWORK] for token handling. Provide clear code examples, diagrams where helpful, and emphasize real-world scenarios. Tailor the guide for [BEGINNER/INTERMEDIATE] developers looking to implement JWT securely.