dsh-plateau: Fat Loss Plateau Calculator

`dsh-plateau` is a plugin for DeepSeek Harness (DSH) that provides agents with parameter-based, precise fat-loss calculation capabilities. Implemented purely in Node.js with no network dependencies, it focuses on numerical calculations in lifestyle-assistance scenarios. Developers can install it using the `dsh plugin add` command and invoke the `plateau` tool in DSH sessions to process health data. The plugin is released under the MIT License, and its execution permissions are scoped to the DSH process.