Improve search for missing vocabularies

For example, searches in languages and funders are still good enough.
![languages](https://github.com/user-attachments/assets/ad2a4ef8-9775-45c9-9127-668ab3f0d9d6)

![funders](https://github.com/user-attachments/assets/b551a0f2-02d9-45e7-b565-0496cb9e8d3f)

See also https://github.com/inveniosoftware/invenio-vocabularies/issues/387