STAMFORD — Judith Martin, the wife of Mayor David Martin and an educator in the city’s public schools, died Thursday following a battle with cancer. Martin was also executive director of Starfish Connection, a nonprofit she founded with her husband that provides long-term academic support for students from low-income families. Starfish mentors students over 10 years, from third grade until they graduate high school. Before becoming a teacher, Martin spent 20 years working in strategic planning, human resources and marketing for companies including Pitney Bowes and ConRail. Janet Schneider, a former assistant principal at Westover Magnet Elementary School, took over as executive director of Starfish Connection last month.