feat: add SQLite-based persistent recipe cache for faster startup

Introduce a new PersistentRecipeCache service that stores recipe metadata in an SQLite database to significantly reduce application startup time. The cache eliminates the need to walk directories and parse JSON files on each launch by persisting recipe data between sessions.

Key features:
- Thread-safe singleton implementation with library-specific instances
- Automatic schema initialization and migration support
- JSON serialization for complex recipe fields (LoRAs, checkpoints, generation parameters, tags)
- File system monitoring with mtime/size validation for cache invalidation
- Environment variable toggle (LORA_MANAGER_DISABLE_PERSISTENT_CACHE) for debugging
- Comprehensive test suite covering save/load cycles, cache invalidation, and edge cases

The cache improves user experience by enabling near-instantaneous recipe loading after the initial cache population, while maintaining data consistency through file change detection.

Author: willmiao