Public Enemy has returned with a blistering new surprise album, “Black Sky Over the Projects: Apartment 2025,” a defiant 12-track collection that fuses the group’s signature social commentary with a fresh dose of old-school fire. Released without advance notice, the record is available on a “pay-what-you-want” basis for 72 hours, giving fans unprecedented access to the group’s most urgent work in years. “These new tracks are for you to get down to at home,” said Flavor Flav, who joins Chuck D at the forefront of the release. “Pay whatcha want for the next 72 hours.”