(Bloomberg) — Six months’ salary in a single day. That’s the kind of payoff China’s boom in initial public offerings is handing to a lucky few.Seven new listings this year have generated profits of more than 100,000 yuan ($14,900) for retail investors who secured an allocation of 500 shares and sold on debut day, the most such windfalls in at least six years. Stacy Wei did even better: her winning bid for Unitree Robotics earned her about 380,000 yuan, enough to upgrade to her dream car.Wei, who works in education in one of China’s biggest cities, beat odds of one…