dsh-web-submit: Driving a Running dsh Web Instance via the CLI

The `dsh-web-submit` plugin for DeepSeek Harness (DSH) addresses the disconnect between CLI and Web UI operations. It provides HTTP interfaces that allow developers to drive a locally running web instance from the command line, with tasks executed inside the web process and reflected in the web UI in real time. Core features include submitting tasks via `POST`, querying status via `GET`, and receiving an SSE event stream via `GET`. Installation requires the `dsh plugin add` command and restarting the web service. It is suitable for local development and debugging scenarios; requests are limited to the local loopback address, and operations requiring permission approval must be confirmed in the web UI.