dsh-ui-notify: Completion Sound Notification Plugin for DeepSeek Harness Web GUI

`dsh-ui-notify` is a standalone Web plugin for DeepSeek Harness (DSH), designed to address the challenge of users noticing when background session output has completed. The plugin provides auditory feedback by playing built-in notification sounds, and all configuration is stored in the browser's `localStorage`. Core features include automatically playing completion sounds, volume adjustment, and selecting the trigger scope (background only or any session). It relies entirely on browser-side rendering and is independent of host services. Users can configure it flexibly through the DSH settings menu. After installation, the Web Profile must be restarted for the plugin to take effect.