The smartest thing Facebook has done since going public is to schedule tomorrow’s mystery announcement. The move pushed the stock price up with optimistic speculation, and gave the company a bonanza of media coverage. But actually holding the event? That could turn out to be the worst misstep yet.That’s because the most persistent rumor about what will play out tomorrow is a losing scenario. Signals abound that CEO Mark Zuckerberg will unveil a Facebook smartphone, plunging the company into the shark tank that is the consumer electronics ?industry.