dsh-luna-vision-bridge: Add Native Image Input Support for DSH

`dsh-luna-vision-bridge` is a host-side DSH LLM plugin designed to overcome the image input limitations of the native input box. It registers a new `luna-vision-bridge` provider to intercept the `addImages` and `submit` workflows: user-uploaded images are transcribed into text via Codex Luna, and the resulting text is passed to a configured downstream plain-text model. The plugin supports native interactions such as pasting and drag-and-drop, provides a web-based configuration interface, but relies on the Codex CLI in the host environment.