ISLAMABAD — U.S. peace envoy Zalmay Khalilzad arrived in Pakistan on Thursday, the last leg of a regional tour aimed at finding a negotiated conclusion to Afghanistan’s 17-year war, which would end the U.S.’s longest military engagement. Khalilzad has accelerated efforts to end the war since his appointment in September. On his previous visits he held talks with the Taliban in their Middle Eastern headquarters in Qatar, but a Taliban official said Khalilzad canceled meetings originally scheduled for Jan.