dsh-model-picker-plus: Enhanced DeepSeek Harness Model Picker

The `dsh-model-picker-plus` plugin is designed to address the challenge of model selection in DeepSeek Harness (DSH) multi-provider scenarios. It replaces the native selector, offering features such as collapsible provider groups, search, favorites, history, and capability tags (e.g., Free/Vision), as well as capability-based filtering. Its layout is compatible with native components and does not encroach on the space used by other plugins. The plugin is fully standalone, does not rely on data from other plugins, runs through DSH's own services, is developed purely on the client side, and supports installation and uninstallation via npm.