Introducing the DeepSeek Harness Model Navigator Plugin

The `dsh-model-navigator` plugin for DSH (DeepSeek Harness) is designed to replace the original model selector. By providing enhanced search, categorization, and state management features, it addresses the challenges of fragmented model discovery across multiple vendors and cumbersome model switching. The plugin reuses host configurations and supports global cross-vendor search, model family grouping, one-click toggling of thinking intensity, and favorites management. Open-sourced under the MIT License, it must be installed while keeping the official model selection plugin enabled, delivering a more intuitive and efficient model navigation experience.