AKM123HKM/Paint3 ? reverse-engineered prompt

Build me a simple desktop paint app in C++ using SFML, with a small reusable UI library built into the same project.

I want the main app to let me draw with a pen tool and erase with an eraser, and to work with layers so I can separate parts of the drawing. The interface should have basic controls like buttons, a scrollbar, and simple grouped UI elements, since I’d like this to feel like a real little paint program instead of just a blank canvas.

Keep it clean and usable, and make the UI feel responsive. If you need to look up current SFML docs or best practices while putting it together, go ahead.