dsh-vision-toggle: Add a Per-Model Image Input Toggle for DeepSeek Harness

The `dsh-vision-toggle` plugin provides a graphical solution for DeepSeek Harness (dsh), eliminating the need to manually edit `settings.yaml` to enable a model's image input. It allows the vision input toggle to be managed independently for each model, loads routed models and applies changes immediately, and supports Chinese and English. After installation, you must restart the application, and it is only applicable to models under the `llm-pi-ai` route.