dsh-done-notifier: macOS Notification When a Model Completes

`dsh-done-notifier` is a macOS client plugin designed specifically for DeepSeek Harness (DSH). It addresses the issue of users missing model replies while working on other tasks. When the model transitions from `running` to `idle`, the plugin displays a macOS banner notification and plays a child-voice chime. It features zero dependencies, duplicate-trigger prevention, and conversation filtering. Users can install it via CLI and customize the notification text and audio file.