Detroit-based developer The Platform on Thursday celebrated opening a $60 million development it calls the first new residential construction of its size in the New Center neighborhood in three decades. Peter Cummings, executive chairman and CEO of The Platform, and Mayor Mike Duggan were among speakers at an event Thursday morning unveiling the 356,000-square-foot development with a mix of 231 apartments. It also has 17,500 square feet of retail, including a Comerica Bank branch that opened Nov. 12 on the development’s ground floor, replacing its location in the nearby Fisher Building.