City and state leaders on Thursday celebrated the completion of 30 Haven, a smart-growth project that includes 53 one- and two-bedroom residential units and 23,000 square feet of retail space, with a ribbon-cutting ceremony that was attended by Greg Bialecki, state housing and economic development secretary, and Town Manager Peter Hechenbleikner. The project was completed by Oaktree Development LLC, a Cambridge-based company that focuses on ecofriendly construction methods and uses green materials, such as environmentally sensitive mechanical systems and high-efficiency appliances.