“Summer: The Donna Summer Musical” is a flat and soulless jukebox tribute to the “Queen of Disco” that disgraces the genre she created by offering thin orchestrations, inauthentic choreography, and a song listing that includes too many obscure cuts from later in her career.  LaChanze’s radiant performance is not enough to salvage this joyless and unfocused show.  Save your money and listen to Summer’s iconic songs instead.