dsh-sound-notifier: DeepSeek Harness Interactive Notification Sound Plugin

`dsh-sound-notifier` is a Web UI plugin for DeepSeek Harness (DSH) that synthesizes sounds via the Web Audio API to address the challenge of noticing state changes during agent development. The plugin plays distinct notification sounds upon message receipt, thinking initiation, tool calls, and turn completion, and supports custom sound configuration through `client.js`. Functionally, only top-level sessions produce sounds, and refreshing the page does not replay them, although the plugin has an approximately 400 ms polling delay and is subject to browser autoplay policy restrictions.