dsh-price-calc: Pricing Calculation

The DeepSeek Harness plugin `dsh-price-calc` is a pricing calculation tool implemented in pure Node.js with no network dependencies. After installation via the command line, developers can directly invoke the `price_calc` tool within a session to obtain business projection results for a small shop. The plugin is suitable for offline or network-restricted environments, but note that it runs with the permissions of the current process; the source code and license should be reviewed before installation.