dsh-age-calc: DeepSeek Harness Age Calculation Plugin

DeepSeek Harness introduces the `dsh-age-calc` plugin, designed to address the frequent need for age calculation in agent development. Implemented in pure Node.js, it runs entirely locally, has no network dependencies, and is fast and stable. The installation command is `dsh plugin add github:uckkk/dsh-age-calc`. Once enabled, the plugin directly registers a tool for DSH sessions to use, making it suitable for scenarios such as user profile analysis. When using it, be mindful of permission risks, ensure that environment dependency versions are correct, and review the source code to verify logical safety.