DeepSeek Harness (DSH) Plugin: dsh-vertex-argon

`dsh-vertex-argon` is a DeepSeek Harness plugin tailored for the Google Gemini 4 Argon model, supporting dual-channel access via Google Vertex AI and the Gemini API. The plugin resolves the HTTP 400 error in the built-in adapter, natively supports three thought levels, thought summaries, v1beta1 long-text continuation, and multi-turn tool-call signing, and automatically sanitizes invalid parameters. Users can install it via CLI or a command, configure the Vertex AI or Gemini API channel as needed, and adjust parameters such as thought level, long decoding, and context window on the settings page.