dsh-model-accordion: Provider Accordion Model Selector

`dsh-model-accordion` is a Web UI plugin for DeepSeek Harness (DSH), designed to address the limitations of a single-view model selection interface. It provides a hierarchical model list and reasoning mode configuration through a collapsible Provider structure. The plugin supports reading reasoning options from model metadata, custom configuration, and adapting to both light and dark themes. Currently, its interface text is in English, and it serves only as a UI component that enhances Web interaction without affecting backend services.