By Nandita Bose and Pavel Polityuk KYIV (Reuters) -Russia’s President Vladimir Putin marked his 70th birthday on Friday with little fanfare, amid further signs that key parts of his invasion of Ukraine were unravelling and triggering unprecedented criticism at home. News programmes made only glancing references to the birthday and public events were low key – in contrast to just a week ago when Putin held a huge concert on Red Square to proclaim the annexation of nearly a fifth of Ukrainian land. On the world stage, in a clear repudiation of Putin’s record, the Nobel Peace Prize was awarded to…