dsh-stain-removal: Stain Removal Methods

DSH’s `dsh-stain-removal` plugin is designed to address the maintenance challenges of hardcoded agent logic. It provides a `stain_removal` tool that returns specific stain-removal recommendations based on input parameters. Users can install it with the `dsh plugin add` command without manual configuration. Implemented purely in Node.js and requiring no network access to run, the plugin provides a standardized interface for agents to handle specific scenarios.