dsh-image-serve: A Local File Display Plugin for DeepSeek Harness

The `dsh-image-serve` plugin registers the `/ws` route to map local absolute paths to web-accessible URLs, solving the issue where DSH Web cannot directly render local screenshots and AI-generated images. The plugin supports cross-platform usage, directory browsing, and UNC network paths. After installation, users need to replace the `file:` protocol in Markdown with `http://127.0.0.1:3080/ws/` followed by the absolute path. Note that the plugin has no whitelist restrictions; if the web interface is exposed to remote access, it may pose a security risk.