Corrects the deserialization of defaultAIModel to ensure it is properly converted from dynamic to Map<String, Object?>. Also fixes a typo in the serialization key from 'defaultLLMSaveObject' to 'defaultAIModel'.
Replaces the previous placeholder for default LLM selection with a working default AI model selector in settings. Updates SettingsModel and related providers to support storing and updating the default AI model as a JSON object. Integrates the selector UI and ensures new AI requests use the default model if set.