Move reverse-migration logic from get_model_folder() (hot path, called on
every metadata/example-images request) to ExampleImagesMigration, where it
runs once at startup. On network storage this was causing 22-38s delays
per LoRA card click.
Additionally optimize prune_stale_example_images() to read the directory
listing once instead of per image entry (O(N*M) → O(M)). Also reorder
consolidation checks so regex filters run before filesystem stat calls.
- Replace setdefault with get and explicit dict initialization in MetadataUpdater
- Change civitai field type from Optional[Dict] to Dict[str, Any] with default_factory
- Add None check and dict initialization in BaseModelMetadata.__post_init__
- Ensures civitai data is always a dictionary, preventing type errors and improving code reliability
