dsh-agent-notify: Windows System Notification Plugin for DSH Web GUI

`dsh-agent-notify` is a browser-side notification plugin designed specifically for the DSH Web GUI, maintained by chidaic and licensed under the MIT License. This plugin aims to address the difficulty of detecting agent status changes during background execution. It pushes events such as task completion, waiting for an answer, approval, or review to the Windows Notification Center via the browser `Notification API`, alerting users via bubble notifications without relying on in-page popups or synthetic audio. Core features include monitoring session state changes to trigger appropriate notifications; notification content consists of the session title and a summary of the last assistant reply (displayed only when the window is open); and it supports three modes: "Do not send," "Send when backgrounded," and "Always send," with "Always send" being the default. The plugin features an anti-false-positive mechanism to prevent replay events after reconnection.