My manager takes credit for everything I do and I am tired

I have been at this company for three years. Every report I write, every idea I present, every client I save — my manager presents it upstairs as his own work. Last week I solved a crisis that would have cost the company a major client. In the all-staff meeting he stood up and said I handled it. Not even a mention of my name. I have screenshots of every email. I am building a case. But part of me just wants to resign and take everything I know to a competitor. What would you do?