WASHINGTON — Secretary of State Hillary Rodham Clinton, at times emotional and fierce, insisted on Wednesday that the department is moving swiftly and aggressively to strengthen security at U.S. missions worldwide after the deadly Sept. 11 raid on the consulate in Libya that resulted in the death of a Grass Valley native. In her last formal congressional testimony on Capitol Hill as America’s top diplomat, Clinton once again took full responsibility for the department’s missteps leading up to assault at the U.S. Consulate in Benghazi, Libya that killed Ambassador Chris Stevens, who was born in Grass Valley. Three other Americans …