Summer heat turns gadget makers’ minds to chilly winter days, when shoppers buy millions of iPods and sleek TVs, but consumers may be lukewarm to this year’s newest crop of gizmos. As they vie for a bigger slice of a global market estimated at $135 billion, leading consumer electronics makers are already showing off their wares — from advanced products such as Nokia’s N91 multimedia mobile phone to novelties like iRobot’s kitchen floor-cleaning robot.