Home prices in major U.S. cities have risen for the first time in eight months, boosted by an annual flurry of spring buyers.The Standard & Poor's/Case-Shiller home-price index reported Tuesday that prices rose in 13 of the 20 cities tracked. Washington, D.C., saw the biggest price increases, followed by San Francisco, Atlanta and Seattle.Still, six metro areas are at their lowest levels in the nearly four years.