This example demonstrates how React state can drive an interactive SVG visualization: a single circle follows the mouse cursor across a 960x500 viewport. On every mousemove event on the SVG, the `handleMouseMove` callback updates the `mousePosition` state with the cursor’s client coordinates, and React re-renders the circle’s `cx` and `cy` attributes accordingly. It uses React 16.9 with hooks (`useState`, `useCallback`) and renders directly to SVG via `ReactDOM.render`.