dsh-plugin-notify: Notification Egress Plugin for DSH

dsh-plugin-notify is a DeepSeek Harness plugin designed for the Windows environment, aimed at addressing the issue where users cannot receive timely updates on the Agent's status when away from the computer. It enables the Agent to invoke the `notify_user` tool by injecting system prompts, supporting proactive notifications upon completion of long-running tasks, errors, or when confirmation is required. The plugin provides an automatic fallback mechanism, including automatic alerts on session errors, desktop notifications at the end of turns, and Chinese voice calls when there is no interaction within a timeout period. Notification channels cover desktop pop-ups (toast), Chinese speech announcements (speak), and system alert sounds (sound), and support four synthetic sound effects such as "explosive" and "victory." Users can manually send notifications via the `/notify` command and adjust settings through environment variables or the configuration panel.