Miranda Lambert grinned as she stood on the smallest stage she’s played in years. She’d just debuted an irreverent, rowdy hook—“Are we in love, or are we just drunk?” from “Bitch on the Sauce (Just Drunk)”—to the thrilled screams of 180 dedicated fans, who were mostly decked out in Miranda shirts, sparkles, fringe, or all three. They had spent hours in the August heat, waiting for the intimate show at Stubb’s Bar-B-Q, in Austin, the same spot where Lambert had played her first major-label showcase, almost exactly twenty years ago.“It was the first time I drank a beer onstage. I was underage, but I was nervous,” she told the audience. Dressed in boots, a cowboy hat, a denim skirt, and a tight black T-shirt bedazzled…