dsh-system-net: Make DeepSeek Harness Follow System Network Settings

`dsh-system-net` is a Node.js plugin that addresses network connectivity issues in DeepSeek Harness (DSH). By reading Windows system proxy settings and merging the operating system's certificate store, it fixes connection timeouts or certificate verification failures caused by routing and certificate trust issues. The plugin supports zero configuration and takes effect after installation without requiring a restart or environment variable setup. Key features include taking over system proxy routing, trusting the system certificate store, and automatic detection. It is suitable for scenarios where tools such as Watt Toolkit are in use, the browser works normally, but DSH cannot access the internet. After installation, restart DSH to make the plugin take effect.