SEOUL, South Korea — North Korean leader Kim Jong Un observed sea trials of a new warship repaired after a failed launch last year and vowed to accelerate efforts to build a nuclear-armed navy, state media said Saturday, showcasing his expanding military capabilities ahead of a visit by Chinese leader Xi Jinping. North Korea’s official Korean Central News Agency said Kim visited the 5,000-ton destroyer Kang Kon on Thursday as it underwent capability tests. Photos released by the agency showed him accompanied by his increasingly prominent teenage daughter, believed to be named Kim Ju Ae, whom South Korean officials say...