dsh-http-probe: HTTP Probe Tool for DeepSeek Harness

The DeepSeek Harness (DSH) plugin `dsh-http-probe` provides the Agent with lightweight HTTP probing capabilities. Using the `http_probe` tool, it allows the Agent to retrieve only the status code, latency, and response headers of an HTTP(S) endpoint without downloading the full response body, making it ideal for API health checks. Since the plugin is not published to npm, it must be installed directly from a GitHub URL. Once installed, the Agent can directly use this tool to probe the connectivity of any endpoint.