sApple declined to comment beyond the e-mailed invitation, which said: "Wish we could say more."Now the Cupertino, Calif.-based company will attempt to repeat that feat in wearables, an emerging group of devices that track people's activity and health. Apple will introduce a wearable gadget along with new iPhones on Sept. 9, a person with knowledge of the plans said. Notices for the event, which will also take place in Cupertino, were sent out today.While companies such as Fitbit and Jawbone have made some headway introducing wearables to the public, global sales of the activity trackers hi...