Michele L’Hommedieu Hofmann had no idea until retiring last fall and starting to research her family history how prominent a role her great-great-grandfather James H. L’Hommedieu had played in Long Island’s late-19th-century architecture. On a trip to New York that included a stop at an East Hampton house he designed for Robert Southgate Bowne, a founder of the Maidstone Club and first president of the Long Island Rail Road, she and her family got a crash course in L’Hommedieu’s work.