LONDON — Keir Starmer’s plans to cement his legacy have been thrown into disarray, with promises to bolster defense spending and reset EU relations now looking highly uncertain as he enters a transition period before handing off to another Labour leader. The outgoing British prime minister will travel to international engagements with the responsibility of office but none of the power, while a question mark hangs over the intentions of his likely successor, Andy Burnham. Starmer announced