Don't treat API-level 401 as session expiry in suggestions functions.
getServiceToken already throws SessionExpiredError when the PDS rejects the service auth request, which propagates before the API call happens. If getServiceToken succeeds but the API returns 401 (wrong API_DID, clock skew, etc.), the user's PDS session is still valid — calling signOut() would revoke it unnecessarily. Surface these as generic errors instead, consistent with listPublications and listSubscriptions.