dsh-pro-vision-std: Portable DeepSeek V4-Pro Image Processing ModelProvider

`dsh-pro-vision-std` is a plugin for DeepSeek Harness (DSH) designed to add image processing capabilities to models. It is rewritten based on the `dsh-std` specification and supports image attachments by first invoking a vision model to generate a description, then using V4-Pro to perform text generation. As a standalone ModelProvider, it is compatible with DSH core logic and supports in-process caching and contract integration. Installation requires the `@dsh-std/adapter-dsh` dependency and provides the route `dsh-pro-vision / deepseek-v4-pro` to enable image-and-text capabilities, without affecting official plugins.