Tens of thousands of American real estate agents are scrambling for supplemental income as a prolonged housing market freeze strips commissions bare, pushing some of the country's 1.4 million licensed Realtors into classrooms, retail floors, and substitute teaching rosters just to stay afloat. The numbers tell a punishing story. A Redfin executive told attendees at the Inman Connect conference that approximately 71% of agents registered on Multi…