* feat: Enhance ModelPickerWidget for Ollama integration
- Implemented a sentinel row for "Custom Ollama model..." in ModelPickerWidget, allowing users to input arbitrary model names.
- Updated action handling in ModelPickerWidget to manage transitions between list and input modes.
- Added async model discovery for Ollama models, integrating with the /model command to fetch locally installed models.
- Created tests for Ollama model discovery and ModelPickerWidget behavior, ensuring proper functionality and user experience.
- Refactored validate_ollama_connection and discover_ollama_models for improved error handling and response management.
* fix: Simplify code by removing unnecessary line breaks in ModelPickerWidget and test cases
* fix: Restore globals on set_chat_model failure to prevent half-switched session
* fix: Improve error handling in ModelCommand by restoring globals on failure
* fix(chat): resolve model switch lag by tracking model/provider key for cache invalidation
* style: format set_chat_model function for improved readability
* fix(chat): improve model switching logic to prevent unnecessary cache rebuilds
* fix(model): ensure globals are restored on agent load failure to prevent model switch issues
X-iZhang