dsh-heatstroke: Heatstroke First Aid Plugin

`uckkk/dsh-heatstroke` is a lightweight, network-independent plugin designed specifically for DeepSeek Harness (DSH). Implemented in pure Node.js, it provides a `heatstroke` tool that returns key first-aid steps for heatstroke in different scenarios. The plugin aims to address the challenge of obtaining first-aid information in offline environments for agents. Once installed, it can be invoked in a session, but users should note the plugin’s runtime permissions and the disclaimer that the first-aid content is for reference only.