fix(persistent-cache): persist scanner cache after model deletion

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

py/services/model_lifecycle_service.py

@@ -111,6 +111,11 @@ class ModelLifecycleService:
             self._scanner._hash_index.remove_by_path(file_path)
 
         await self._sync_update_for_model(model_id)
+
+        persist_current_cache = getattr(self._scanner, "_persist_current_cache", None)
+        if callable(persist_current_cache):
+            await persist_current_cache()
+
         return {"success": True, "deleted_files": deleted_files}
 
     @staticmethod