dsh-plugin-grok: DeepSeek Harness Plugin for Locally Driving the Grok Build CLI

`dsh-plugin-grok` is a developer preview plugin for DeepSeek Harness (DSH) that drives the local Grok Build CLI as a tool, providing models with text, image, and video generation capabilities. Instead of relying on HTTP calls, the plugin directly executes the local `grok` binary and supports authentication via `grok login` or `XAI_API_KEY`. Usage requires proxy configuration and interacts with the three exposed tools: `grok_ask`, `grok_imagine_image`, and `grok_imagine_video`. Video generation works by first producing a static image and then converting it into a video. The plugin is currently released as a developer preview under the MIT license.