Make sure a contact has Alma's initial briefing

Written once per contact, when the memory sweep finishes. This endpoint is the safety net for contacts imported before briefings existed, and for sweeps where that call failed. It does NOT consume the weekly Alma quota: nobody asked a question. It cannot be used to spend either, because at most one briefing entry exists per contact (a partial unique index), and a caller that does not claim that slot never reaches the model. building means the contact's memory is not ready yet, which is the honest answer rather than a briefing about an empty sheet.