dsh-mobile-push-notify: Task/Goal Completion Notifications (Desktop Native + Mobile Web Push)

The DeepSeek Harness (DSH) Mobile Push Notification plugin is designed to address the issue of background task status not being accessible in a timely manner. It provides native desktop notifications for macOS, Windows, and Linux, and supports zero-configuration phone PWA/Web Push pairing to achieve lock-screen synchronization. Users can install it with `dsh plugin` and pair their phone using the built-in Cloudflare tunnel, even without a public IP. The plugin consists of three independent modules: desktop notifications, gateway/tunnel, and push, all configurable via environment variables. Its security model uses internal network isolation and access control to ensure encrypted push and accept loopback requests only, with additional risks to consider only when using a public tunnel.