A hedge fund manager who has been sued by his own mother over an unpaid mortgage he took out on her house has declared himself bankrupt — just months after The Post exposed his wild spending spree in the south of France. Jason Ader — a 59-year-old former activist investor who a decade earlier regularly appeared on CNBC and helped unseat Marissa Mayer as CEO of Yahoo — quietly filed for personal bankruptcy in Miami on Dec. 22, according to court documents reviewed by The Post. He owes roughly 2 million in debts, he admitted in court filings and a...