DSH-Vision-Plugin: Adding Image Understanding Capabilities to DSH

dsh-vision-plugin is a plugin developed specifically for DeepSeek Harness (DSH), designed to address the limitation that pure text models cannot directly process images. This plugin leverages OpenRouter's free multimodal models (`:free`) to automatically convert images into text descriptions before sending, thereby endowing text-based models like DeepSeek with image understanding capabilities, all at zero API cost. Key features include: providing a `describe_image` tool to read local images; intercepting and converting images automatically via the `llm/stream` hook when the model does not support image inputs; and automatically writing a `deepseek-vision` provider pointing to OpenRouter into the configuration file on first startup.