follow the cursor
A single circle follows the cursor within an SVG canvas, its position updating in real time. The visualization uses React’s `useState` and `useCallback` to manage mouse-move events, while D3.v7 supplies the SVG rendering via `d3.min.js`. The circle’s center coordinates (`cx`, `cy`) are set from the pointer’s `clientX` and `clientY` values, producing a direct, interactive response.