dsh-ab-sample: A/B Testing Sample Size Calculator

Developers using DeepSeek Harness (DSH) can use the `dsh-ab-sample` plugin to calculate A/B test sample sizes locally, without an internet connection and with precise results. The plugin is implemented purely in Node.js, provides the `ab_sample` tool, supports receiving test parameters, and returns detailed calculation results. Usage requires the dependencies `@deepseek-ai/cordis` (^4.0.1) and `@deepseek-ai/dsh-tools` (>=0.1.0-rc.6). The installation command is `dsh plugin add github:uckkk/dsh-ab-sample`, making it suitable for developers who need quick statistical calculations.