dsh-hot-reload: Hot Reloading for DeepSeek Harness Plugins

The dsh-hot-reload plugin addresses the need to restart DeepSeek Harness (dsh) when upgrading plugins. It enables hot reloading by watching `pnpm-lock.yaml`, and supports safe rollback, state persistence, and result reporting. Before use, install the plugin and restart dsh; afterward, plugins can be upgraded directly without a restart. The plugin requires dsh 0.1.0-rc.6 and Node.js 22+, making it suitable for development scenarios that require frequent iteration of plugin logic.