dsh-poisson-pmf: Poisson Distribution Calculation Plugin

`dsh-poisson-pmf` is a DeepSeek Harness (DSH) plugin for calculating the probability mass function of the Poisson distribution. Maintained by user uckkk, it is a pure Node.js mathematical computation module with no network dependencies, suitable for handling discrete probability distributions in agents or workflows. The plugin is released under the MIT license and requires the `@deepseek-ai/cordis` and `@deepseek-ai/dsh-tools` dependencies.