MCPServer: replace databaseInterface with Django models

`databaseInterface` is still imported in a few places in MCPServer, primarily for the `getUTCTime` function that will be moved elsewhere, and for database locking that may be removeable.
If we're not evaluating the queryset, [```.exists()```](https://docs.djangoproject.com/en/dev/ref/models/querysets/#exists) seems to be better.