dsh-windows-notifications: DSH Web Windows Desktop Notification Plugin

# Introduction When running long tasks on DeepSeek Harness (DSH), users rarely stay on the DSH web page. Switching to other windows to write code or read documentation, they only find upon returning that the task has long since completed or is stuck waiting for approval, having run idle for a long time in between. Events within DSH Web are only displayed on the page itself; if you don't keep the tab open to monitor it, they are easily missed. The `dsh-windows-notifications` plugin introduced below fills this gap: it keeps the DSH tab open and ensures that while you work in other applications, task results and events of interest can still reach you in the form of Windows desktop notifications, in-page cards, and optional sounds. # What is dsh-windows-notifications