Billionaire hedge-fund manager John Paulson maintained his holding in the world’s biggest exchange-traded product backed by gold as prices posted the best first half in almost four decades. At the end of June, Paulson & Co. owned 4.8 million shares of SPDR Gold Shares, a U.S. government filing showed. That was unchanged from the end of March, when the firm cut its stake for a second straight quarter. Gold futures have climbed 27 percent...