- Add SQLAlchemy database setup with session management
- Add Job model with status, priority and progress tracking
- Add QueueManager with priority queue and deduplication
- Add SystemSettings model for database-backed configuration
- Add SettingsService with caching and defaults
- Add SystemMonitor for CPU/RAM/GPU resource monitoring
- Add LanguageCode utilities (moved from root)
- Add backend/config.py with Pydantic settings validation
- Support for standalone, provider, and hybrid operation modes
- Multi-database backend configuration (SQLite/PostgreSQL/MariaDB)
- Environment variable validation with helpful error messages
- Worker and Whisper model configuration
