dsh-model-cascade: Three-Tier Model Selector for DeepSeek Harness

The DSH plugin `dsh-model-cascade` refactors the model selector in the bottom-right corner into a three-level cascading menu, addressing the low lookup efficiency caused by an expanded model library. Core features include a three-level hierarchy, breadcrumb navigation, independent thinking intensity settings, state synchronization, and automatic hiding of the built-in list. Installation requires placing the files in `node_modules` and modifying the configuration file. The plugin depends on DSH 0.1.5-rc.1, but has limitations such as series grouping logic relying on heuristic splitting, hardcoded styles, and sub-agent sessions not being rendered.