Build a DDQN Snake Game with TensorFlow.js in a Single HTML File

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 {{canvas_width|400}}, {{canvas_height|400}} for configurable options.
• Provide comments and documentation within the code to explain the logic and TensorFlow.js usage.