China's factory activity returned to growth in September, offering a modest sign of improvement for the world's second-largest economy as easing weather disruptions and strong demand linked to the global artificial intelligence boom supported industrial production.The official manufacturing purchasing managers' index (PMI) rose to 50.1 in September from 49.8 in August, moving back above the 50-point threshold that separates expansion from contraction, according to data from China's National Bureau of Statistics. The reading matched the median forecast in a Reuters poll. The improvement ended two consecutive months of contraction.Read more: Global Market: Japan’s Nikkei rises as AI stocks track US…