GABRIELLE TETRAULT-FARBER and TOM BALMFORTH POLICE detained more than 2,000 people and used force to break up rallies across Russia on Saturday as tens of thousands of protesters ignored extreme cold and police warnings to demand the release of Kremlin critic Alexei Navalny. Navalny had called on his supporters to protest after being arrested last weekend as he returned to Russia from Germany for the first time since being poisoned with a nerve agent he says was slipped to him by state security agents in August. The authorities had warned people to stay away from Saturday's protests, saying they risked…