dsh-better-model-selector: Split Model Selection and Thinking Intensity Controls

The `dsh-better-model-selector` plugin optimizes the DSH web interface by separating the model selector and thinking intensity selector into independent components. The model selector adds search and favorites functionality, while thinking intensity is adjusted using a slider. The plugin supports keyboard shortcuts (Ctrl+P to switch models and Ctrl+T to adjust intensity) and fixes the favorites list persistence issue when the port changes. Installation requires the DSH Next channel. Note that the controls are displayed only for specific models or sessions, and favorites data is stored in host-level cookies.