A React component renders a single SVG circle that follows the mouse cursor across the full browser window. The app tracks pointer coordinates via an `onMouseMove` event handler, storing them in state with the `useState` and `useCallback` hooks. As the mouse moves, the circle’s `cx` and `cy` attributes update reactively, producing a direct visual tracking effect. The example demonstrates declarative SVG rendering with React’s virtual DOM, using no external charting library.