North Korean leader Kim Jong Un toured a Russian factory that makes fighter jets, as the U.S. warned he is on a visit that could support the Kremlin’s assault on Ukraine. Kim arrived in the eastern city of Komsomolsk-on-Amur on Friday to see a facility that makes high-tech fighter jets and other aircraft. He was shown planes including the Su-35 as well as the Su-57 stealth combat fighter,…