dsh-show-image: Send Workspace Images Directly in the WebUI

The `dsh-show-image` plugin allows a model to directly present workspace images (such as rendered images) to the user without manual copy and paste. It registers a `show_image` tool that converts images from the file system into conversation attachments, supports PNG, JPEG, WebP, and GIF formats, and enables preview in the WebUI as a gallery or lightbox. The plugin includes a host side (handling file reading and saving) and a browser side (handling rendering), and supports a `caption` parameter and context isolation. After installation, restart the DSH WebUI; the image path must be a locally accessible workspace path.