dsh-model-collapse: Group and Collapse the Model Selector by Provider

The DSH plugin `dsh-model-collapse` groups and collapses the model selector by provider to reduce the space taken up by long lists. It includes a top quick bar and keyboard shortcuts (such as Alt+E to expand and Alt+F to focus), and supports remembering expanded states and filtering. The plugin is purely front-end, does not modify the official source code, and is released under the MIT license. The repository has been archived; see the official collection for details.