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Create a beautiful floating steampunk train world using Three.js in a single HTML file. 
Include a locomotive with a few train cars moving around floating islands, spinning wheels, animated steam, glowing windows, a waterfall, clouds, and distant mountains. 
Add a “Boost” button to increase train speed and steam output. 
Include basic orbit and zoom controls, atmospheric lighting, and smooth animations. 
Keep the scene visually impressive but lightweight, using simple geometry and optimized effects. 
Deliver the complete working HTML file.