Got window dragging working. The key thing I learned: you have to attach mousemove and mouseup to the document, not to the window element itself otherwise if you move the mouse too fast it slips off the element and the drag breaks.

Added the About, Projects, Contact, and Terminal apps. The About app has a sidebar you can click through, and Projects renders cards from a JavaScript array which made it easy to add new ones. The terminal took the most time.

Also added z-index stacking so clicking a window always brings it to the front, and desktop icons that select on single click and open on double click.