Agence France-Presse: One year after staging a mostly pollution-free Olympics, Beijing has seen its skies shrouded in haze again, highlighting what observers call a mixed Olympic legacy on the environment. Amid fears the city’s chronic smog could damage athlete’s health, Beijing took drastic steps to prevent that last August, moving or cleaning up polluting factories, curbing traffic, and ordering a halt to all construction work. State-of-the-art facilities like the "Bird’s Nest" Olympic stadium and …