dsh-stair-calc: Stair Tread Calculation Plugin

`uckkk/dsh-stair-calc` is a lightweight calculation plugin for DeepSeek Harness (DSH), designed to improve the efficiency of engineering calculations. Maintained by `uckkk` and built with pure Node.js, it has no network dependencies and supports precise calculation of stair treads based on specified parameters. Users only need to run `dsh plugin add github:uckkk/dsh-stair-calc` to install and invoke its tools, making it suitable for offline or specialized environments and helping ensure safe and convenient calculations.