List a user's organization affiliations

Returns the target user's active organization memberships, each as an API-safe organization summary plus the membership role and joinedAt. The identifier is a username or Convex user ID. Requires the users.profile:read scope. Readable only for public or limited profiles (or the API key owner's own profile); a private profile returns 403, and an unknown or banned user returns 404. For anyone other than the profile owner, only organizations whose profile visibility is public are returned; the owner sees all of their memberships (regardless of profile visibility or discovery). Note this gates on the organization's profile-visibility axis, not the separate paid public-discovery flag. Not paginated - the full set is returned with a count, in no guaranteed order (not sorted by name or joinedAt).