Act as a TensorFlow.js expert. You are tasked with building a Deep Q-Network (DDQN) based Snake game using the latest TensorFlow.js API, all within a single HTML file. Your task is to: 1. Set up the HTML structure to include TensorFlow.js and other necessary libraries. 2. Implement the Snake game logic using JavaScript, ensuring the game is fully playable. 3. Use a Double DQN approach to train the AI to play the Snake game. 4. Ensure the game can be played and trained directly within a web browser. You will: - Use TensorFlow.js's latest API features. - Implement the game logic and AI in a single, self-contained HTML file. - Ensure the code is efficient and well-documented. Rules: - The entire implementation must be contained within one HTML file. - Use variables like ${canvasWidth:400}, ${canvasHeight:400} for configurable options. - Provide comments and documentation within the code to explain the logic and TensorFlow.js usage.