In the midst of the Cold War, a young Texan visited Moscow and turned the classical music world upside down. Stuart Isacoff takes us back to 1958 to relive Van Cliburn’s stunning victory at the Tchaikovsky International Piano Competition. His new book is called “When the World Stopped to Listen: Van Cliburn’s Cold War Triumph, and Its Aftermath” (Knopf). The 15th Van Cliburn International Piano Competition begins today in Fort Worth.