refactor: extract ASR configuration management into focused manager classes
- Split AsrConfigService into three focused components for better separation of concerns:
- AsrEngineManager: handles engine lifecycle, model loading, and capability detection
- AsrJobManager: manages job tracking, status updates, and shutdown cleanup
- AsrConfigService: orchestrates configuration changes using the managers
- Moved engine creation, validation, and persistence logic to AsrEngineManager
- Moved job registration