dsh-model-groups: DeepSeek Harness Platform and Vendor-Grouped Model Selector

`dsh-model-groups` is a standalone DeepSeek Harness client plugin designed to optimize the model selection experience in multi-vendor, multi-model scenarios. By reusing existing services and overriding specific slots, it groups and displays models by vendor, while supporting routing unknown models to `Other/platform`. Installation requires configuration through a Profile's Bundle or Patch, and the built-in model plugin must remain enabled. The plugin is released under the MIT License, is an unofficial project, does not handle credentials, and is suitable for users who need fine-grained management of their model lists.