KYIV, Ukraine— Russia fired at least 800 drones in a massive daytime attack Wednesday on about 20 regions of Ukraine, killing at least six people and wounding dozens, including children, President Volodymyr Zelenskyy said. The prolonged barrage began in midmorning and lasted for hours, hitting the capital of Kyiv, the western city of Lviv near Poland, and the port of Odesa on the Black Sea, among other population centers, he said on the Telegram messaging app. “Our soldiers are defending Ukraine, but Russia’s obvious goal is to overload air defenses,” Zelenskyy said, as the bombardment stretched into the late afternoon. He cautioned that a cruise and ballistic missile attack could follow the drone barrage. It was “one of the longest, massive Russian attacks against Ukraine,” he said on social media. Moscow’s attacks on its neighbor are unrelenting, even as Ukraine is emboldened by its recent military accomplishments and as U.S.…