North Korean leader Kim Jong-un vowed to lift living standards as he opened a landmark congress, state media said on Friday, offering a glimpse of economic strains within the sanctions-hit nation. The supreme leader took centre stage with a speech to start the Workers’ Party congress, a gathering that directs state efforts on everything from house building to war planning. Held just once every five years, the days-long congress offers a rare glimpse into the workings of a nation where even...