Greener and roomier with a chic naturalistic look, the Highmark Mann Center officially reopened Monday after the final phase of a yearslong renovation. Construction at Philadelphia’s outdoor arts center in Fairmount Park went not just down to the wire, but a few weeks beyond it, delayed by this past winter’s stretch of snow, ice and subfreezing temperatures. In early June, dance fans arriving for BalletX performances found the main entrance and other parts of the campus still under construction.