dsh-complete-notify: Add task completion sounds and notifications to DSH.

# Introduction When running tasks with DSH (DeepSeek Harness), a common workflow involves handing off the task to an agent and switching to other tasks. The difficulty lies in not knowing when the task will conclude: it may have finished early waiting for your feedback, or be blocked midway requiring approval. Constantly staring at the page wastes attention. `dsh-complete-notify` addresses this issue: it plays a sound and displays a notification when the task completes. It utilizes a toast notification when the page is in the foreground and switches to a system notification when in the background. The following sections introduce its positioning, features, installation, and configuration. # What is this? `dsh-complete-notify` is a DSH plugin maintained by kaixinbaba, licensed under the MIT license. One-sentence positioning: it plays a sound and pops up a small notification when the task is complete.