traffic-light: DeepSeek Harness Session Status Indicator

The `traffic-light` plugin for DeepSeek Harness adds a three-color signal light to the chat input box, providing an intuitive view of session status: green for idle, yellow for generating, and red for errors. It reflects the session snapshot in real time, with details and throughput available on click. The plugin supports accessible interactions, internationalization, and custom configuration, and relies on the `useSession` and `useProjection` APIs from the DSH framework for secure and reliable operation.