dsh-dish-margin: Dish Margin Calculation

The DeepSeek Harness (DSH) plugin `uckkk/dsh-dish-margin` is used to accurately calculate dish gross margins in conversations. The plugin is implemented in pure Node.js, requires no network access, and depends on `@deepseek-ai/cordis` (^4.0.1) and `@deepseek-ai/dsh-tools` (>=0.1.0-rc.6). Install it with `dsh plugin add github:uckkk/dsh-dish-margin`; after installation, you can use it by calling the `dish_margin` tool directly in the conversation.