dsh-win-notify: DSH plugin that pops up a task completion notification with sound on Windows

`dsh-win-notify` is a Windows plugin for DeepSeek Harness (dSH), designed to address the challenge of tracking background agent task status. This plugin triggers Windows Toast pop-up notifications with sound when tasks complete, encounter errors, or await approval/replies, displaying "DeepSeek" as the app name along with the official icon. Its core advantages lie in focused awareness and intelligent interaction: it suppresses notifications when the GUI session is in the foreground; upon clicking a notification, it prioritizes switching to an existing GUI tab via a local micro-assistant, avoiding duplicate new tabs, and relies solely on Windows' built-in PowerShell 5.1 without requiring additional runtimes. Installation is straightforward, and it can be added to a specific profile using the `dsh plugin` command.