dsh-nail-shape: Nail Shape Selection

The DSH plugin `dsh-nail-shape` provides a “nail shape selection” feature, using the tool function `nail_shape` to return a nail care plan based on input parameters. The plugin is implemented entirely in Node.js, has no network dependencies, and is easy to install. It is suitable for DSH workflows that require local logic processing, runs with the current process permissions, and its source code is open source.