DeepSeek Harness Plugin Installation Compatibility Pre-Check Guard (dsh-install-guard)

`dsh-install-guard` is a pre-install compatibility guard for DeepSeek Harness, designed to prevent service crashes caused by version mismatches or missing manifests. The plugin ensures compatibility with the current environment by validating Node versions, peer dependencies, and required manifest fields, and by performing an isolated trial startup. Users can manually invoke the `plugin_install_guard` tool to run compatibility checks and install it, making it a key tool for building a complete pre-installation validation pipeline and reducing the risk of introducing plugins.