dsh-notify-sound: Play a notification sound after the AI finishes replying

`dsh-notify-sound` is an MIT-licensed DSH web plugin designed to address the pain point of users confirming when AI responses are completed. By listening to the `turn/end` event and leveraging WebSocket real-time push, it automatically plays a built-in notification sound at the end of each turn, without requiring polling or online audio loading. The plugin includes 44 optional sound effects (sourced from `Stephanvs/opencode-sfx`), and supports toggling, switching sounds, adjusting volume, and previewing directly in the DSH settings page. Preference settings are stored in the DSH settings service, apply globally, and persist across restarts. Installation requires Node.js >= 20, with support for remote installation from GitHub or local development deployment. Core dependencies include `@deepseek-