fix(app): stale question cards from dead turns — a cleanup path surfaced to the panel #1754

Important

Problem — When a turn dies (abort, wedge, engine cycle), its question card stays up and replies toast errors forever — the card outlives the question. There is no question.replied/question.rejected-equivalent cleanup path surfaced to the panel, and card liveness isn't tied to turn state.
Approach — Either surface a cleanup event family to the panel (replied/rejected/expired equivalents, so the card retires deterministically) or tie card liveness to turn state (turn dead → card dismisses with a clear label). The slice's first job is mapping what the engine already emits vs. what the panel already models — the fix rides existing event vocabulary wherever it exists, inventing nothing new at the engine.
Scope — in: the panel-side cleanup path + tests + headless-probe verification (kill a turn mid-question; assert the card retires or labels dead). out: engine event vocabulary changes, the frontdoor's question map (it already learns + injects; this is panel consumption).