Norphel/joktang · Set `library_name` to `tf-keras`.

Model 'Norphel/joktang' seems to be compatible only with "Keras 2" and not "Keras 3". To distinguish them, models compatible with legacy Keras 2.x should be tagged as tf-keras while models compatible with Keras 3.x are tagged as keras.

This PR updates the model card to replace the explicit library_name: keras metadata which is now outdated by library_name: tf-keras. Updating this metadata will facilitate its discoverability and usage.

For more information about keras and tf-keras library names, check out this pull request: https://github.com/huggingface/huggingface.js/pull/774.