At the start of “Gray Mountain,” John Grisham’s angry and important new novel, Samantha Kofer — age 29, Washington native, graduate of Georgetown and Columbia Law — is a third-year associate at a huge New York law firm. She works 100 hours a week, doing boring chores that she hates, but she’s earning $180,000 a year and expects to be a $2 million-a-year partner by age 35.