dsh-deed-tax: Deed Tax Calculation Plugin

The DeepSeek Harness (DSH) plugin `dsh-deed-tax` is designed for agent development and provides deed tax calculation with a pure Node.js implementation. The plugin runs entirely locally, requires no network access, and can be invoked directly within DSH sessions. Users can install it with `dsh plugin add github:uckkk/dsh-deed-tax`. This solution is suitable for financial tax calculations and agent development in restricted network environments.