Detroit, which has become a near synonym for economic blight and decay in recent years, is starting to show a turnaround. Jobs are coming back and auto sales were good amid disappointing national retail sales numbers in July. Though foreign automakers are still leaner and account for half of all car sales in the U.S., while the slow economic recovery continues to make investors and customers nervous, the way of doing business has changed in the city. Vehicle lineups are streamlined, plus expensive rebates and overproduction are history. The Big Three’s chief executives are all outsiders, focused on making their companies more efficient. The result? Ford made more money in the first half of this year than it did in the previous five years combined. GM is profitable and readying to make a huge public stock offering. And even Chrysler, which looked mortally wounded two years ago, is hiring. Though there’s more work to do, Detroit’s changes look to be permanent.