play_turn now checks level_status before committing: a won or lost
level rejects the swap (accepted=false) with no move spent and no
score change, until restart returns it to in_progress. Adds an
accepted flag to TurnResult so the renderer can show the move was
ignored. Regression in tests/level.sx asserts post-won and post-lost
play_turn leaves score/moves/status unchanged and that restart
re-enables play.
e77c470546