TikTok's chief executive has sought to reassure US Congress that the Chinese-owned video app is not "an agent" of Beijing and poses no risk to national security. Shou Zi Chew faced hours of tough questioning by deputies in the House of Representatives convinced that the popular app is a "tool" of the Chinese Communist Party. Some have also raised concerns that TikTok, which has 150 million American users, carries content that can harm children's mental health. The deputies on the House Committee on Energy and Commerce pressed Mr Chew on various topics – ranging from TikTok's content moderation practices to…