Filter corpora by category

https://redmine.teklia.com/issues/11416

Requires #1596 (closed)

The corpora store should include a new categories getter. It returns an array of unique CorpusCategory found in all the known corpora, ordered by display name.

When the user is an instance administrator, the Category column should have a small <select>, similar to the existing Filter by name… input. This <select> includes an empty option named Filter by category, selected by default, and one option per category listed in useCorporaStore().categories. The filterCorpora method in components/Corpus/List.vue must then filter both by name and by category.