dsh-showme-html: Show HTML in Conversations and Send Back Feedback

The DSH plugin `dsh-showme-html` solves the problem of visual output loss and missing feedback semantics in Agent workflows. It allows agents to render HTML pages as conversation cards, supporting full-screen previews, multiple preset styles, and receipt health checks. Once users provide feedback through the page, the content can be inserted into the input box with one click or appended to a feedback file. The plugin does not introduce a standalone service, stores files by default in a hidden directory, and supports offline use. Interactive scenarios such as design review can be implemented via the `show_html` tool.