dsh-vision-tools: Adding image understanding capabilities to DSH sessions

`dsh-vision-tools` is a visual plugin within the DSH ecosystem, maintained by moon09300731 (MIT License). It provides a global `vision_understand` tool that uses OpenAI-compatible APIs (supporting Zhipu, Alibaba, SiliconFlow, and OpenAI) to understand local images, enabling image descriptions, text recognition (OCR), and image-based Q&A. Images can be sent via paste, drag-and-drop, or button selection; they are automatically saved to a specified directory and filled into the prompt. The plugin supports rate limiting auto-degradation, real-time application of global and project-level configurations, and provides an "Image Recognition" entry in the Web interface. The installation command is `dsh plugin --profile web add dsh-vision-tools`, and `dsh web` needs to be restarted. Configuration requires...