dsh-model-selector: Enhanced Model Selector for DeepSeek Harness

The DeepSeek Harness (DSH) plugin `dsh-model-selector` optimizes the model selection experience through a Shadow mechanism. It provides a single-level collapsible menu, search functionality, and an inference intensity slider, with support for keyboard navigation and accessibility. Installation is simple, with no configuration options, and it depends on the DSH environment. As a purely UI-based tool, it performs no file read/write operations or network requests, making it suitable for users who need efficient model switching and are attentive to inference configuration.