List Caller Pending Memberships

List the organization invitations still awaiting the caller.

The invitee's side of the invitation flow, where /me/member-invitations is the admin's. Not to be confused with GET /me/memberships, which lists the organizations the caller is already an active member of and deliberately omits an invited one.

Takes no token, unlike /api/v1/invitations/*: those are public because the recipient of an emailed link holds nothing else to prove anything with, while this caller is authenticated as the addressee and the membership's own user_id is what scopes the answer. An invitation whose deadline has passed is omitted rather than listed as unactionable.