dsh-stack: Reproducible DeepSeek Harness Environment Setup

`dsh-stack` is a plugin for DeepSeek Harness designed to address non-reproducible environments. By generating a JSON Stackfile that includes plugin order, versions, and configuration patches, it ensures a complete and portable environment context. The tool provides export, inspect, plan, and apply commands, supports secret placeholder management and checksum verification, and enables teams to review environment contracts before applying them, enhancing security.