Workers toil by night lights with hoes, carving out the signs for Olympic rings in front of an unfinished 30,000-seat stadium, bulb-shaped gymnasium and swimming complex in a little-known Chinese city. Loudi, home to 4 million people in Chairman Mao Zedong’s home province of Hunan, is paying for the project with $185 million in bonds, guaranteed by land valued at $1.5 million an acre.