dsh-port: Port Check

dsh-port is a port-checking plugin in the DeepSeek Harness (DSH) ecosystem. It is implemented in pure Node.js with no network dependencies and is designed to integrate port detection capabilities. After installing it with the `dsh plugin add` command, the corresponding tools can be invoked directly in the current session. Before use, ensure that the local environment meets the version requirements of `@deepseek-ai/cordis` ^4.0.1 and `@deepseek-ai/dsh-tools` >=0.1.0-rc.6, and note that the plugin runs under DSH process permissions.