Expired notes should still explain what is missing

Expired handoff notes should stay explainable instead of disappearing silently.

One thing I like in the review-window idea: an expired handoff note should not vanish. It should say what is missing. For example, if a note says a customer case needs a callback by Thursday, the expired state should answer: was the callback done, rescheduled, or still unknown? Without that, hiding the note only makes the next person rebuild context from memory.