feat(model-scanner): add metadata tracking and improve cache management

- Add metadata_source field to track origin of model metadata
- Define MODEL_COLUMNS constants for consistent column management
- Refactor SQL queries to use dynamic column selection
- Improve Civitai data detection to include creator_username and trained_words
- Update database operations to handle new metadata field and tag management

py/services/model_scanner.py

@@ -189,6 +189,7 @@ class ModelScanner:
             'favorite': bool(get_value('favorite', False)),
             'notes': notes,
             'usage_tips': usage_tips,
+            'metadata_source': get_value('metadata_source', None),
             'exclude': bool(get_value('exclude', False)),
             'db_checked': bool(get_value('db_checked', False)),
             'last_checked_at': float(get_value('last_checked_at', 0.0) or 0.0),