After deleting a model, the in-memory scanner cache was updated but the
SQLite persistent cache was not. On server restart, the stale persistent
cache caused check_model_version_exists() to return True, blocking
re-download with 'Model version already exists'.
Add _persist_current_cache() calls in both deletion paths:
- ModelLifecycleService.delete_model() (used by versions tab delete)
- delete_model_version handler in MiscHandlers