🤖 fix: restore model favorites in ChatInput

The ORPC migration PR accidentally removed the model favorites integration
from ChatInput. Restored:
- defaultModel and setDefaultModel from useModelLRU()
- useEffect to reset model to default when entering creation mode
- defaultModel and onSetDefaultModel props passed to ModelSelector

The ModelSelector.stories.tsx WithDefaultModel story documents the feature.

Author: ethanndickson

src/browser/components/ChatInput/index.tsx

@@ -178,7 +178,6 @@ export const ChatInput: React.FC<ChatInputProps> = (props) => {
     [storageKeys.modelKey, addModel]
   );
 
-
   // When entering creation mode (or when the default model changes), reset the
   // project-scoped model to the explicit default so manual picks don't bleed
   // into subsequent creation flows.