Squashed commit of the following:

commit 28e2927e
Author: Grégoire Locqueville <gregoire.locqueville@cnrs.fr>
Date:   Mon Dec 2 17:06:29 2024 +0100

    Deal with error with a proper error

    ... instead of returning a `Maybe` to the frontend

commit 54675ae8
Author: Grégoire Locqueville <gregoire.locqueville@cnrs.fr>
Date:   Mon Dec 2 16:27:03 2024 +0100

    Return Maybe (node ID) upon creating a subcorpus