Build a physics sandbox

the prompt

Build an interactive 2D physics sandbox on an HTML <canvas>. Clicking anywhere drops a circle that falls under gravity and collides — with the floor, the side walls, and other circles — bouncing and settling to rest realistically (position, velocity, restitution). Vary circle size and color. Include a "clear" button and a live count. Vanilla JavaScript only, no libraries. Return one self-contained HTML file. Output only the HTML.

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