WASHINGTON — House Speaker Nancy Pelosi said Thursday that she will not seek a leadership position in the new Congress, making way for a new generation to steer the party after Democrats lost control of the House to Republicans in the midterm elections.Pelosi announced in a spirited speech on the House floor that she will step aside after leading Democrats for nearly 20 years and in the aftermath of the brutal attack on her husband, Paul, last month in their San Francisco home.The California Democrat, who rose to …