dsh-opencode-go-model-list: Fix opencode-go Model List Issue on DeepSeek Harness

The `opencode-go` routing model list in DeepSeek Harness (DSH) often lags behind upstream. The `dsh-opencode-go-model-list` plugin is designed to address this by directly contributing models to the built-in catalog, keeping the list synchronized. It supports extending the routing list, background cache refresh, and offline access. After installation, DSH must be restarted for the plugin to take effect, and it requires a pnpm or PowerShell environment. This tool eliminates cumbersome manual configuration and makes it easier for users to access the latest models.