## Description Add frontend tests for Apollo Client authentication and cache handling. ## Done when - [x] Authentication headers are included in GraphQL requests when a user is logged in. - [x] Authentication headers are removed when no user is logged in. - [x] Apollo cache is cleared when the authenticated user or token changes. - [x] Cached data from a previous user is not reused after logout or account switching. - [x] Relevant cached queries are refreshed or invalidated after mutations.