dsh-trapezoid: A Trapezoid Area Calculation Plugin

The `dsh-trapezoid` plugin for DeepSeek Harness (DSH) is maintained by developer uckkk and provides lightweight trapezoid area calculations in the model inference workflow. It is implemented in pure Node.js, has no network dependencies, and supports offline execution. After installation, users can invoke the tool directly in a DSH session for geometric calculations. Before use, ensure that the environment satisfies the dependency requirements of `@deepseek-ai/cordis` ^4.0.1 and `@deepseek-ai/dsh-tools` >=0.1.0-rc.6.