dsh-tool-notify: DeepSeek Harness Notification Tool

`dsh-tool-notify` is an extension plugin for DeepSeek Harness (DSH) designed to provide agents with a native `notify` tool for notifying external systems when tasks are completed or human intervention is required. The plugin supports two delivery methods: ntfy and webhooks. Installation requires compatible Node.js and pnpm versions, with endpoints and authentication configured via a configuration file. When the model invokes the tool, it can customize the message and priority, and the plugin returns a status object rather than throwing exceptions. Developers should note that it is currently in preview and that build permissions must be configured when installing from source.