By Nandita Bose and Pavel Polityuk NEW YORK/KYIV (Reuters) -Russian President Vladimir Putin’s threat to use nuclear weapons in Ukraine has brought the world closer to “Armageddon” than at any time since the Cold-War Cuban Missile Crisis, U.S. President Joe Biden said. With his seven-month invasion unravelling, Putin celebrated his 70th birthday on Friday with fawning praise from some officials but little public fuss. That was a contrast to just a week ago when he staged a huge concert on Red Square to proclaim the annexation of nearly a fifth of Ukrainian land. In a clear repudiation of Putin…