alyssaxuu/flowy ? reverse-engineered prompt

Build me a lightweight JavaScript library for making flowcharts in the browser, with a simple demo page so I can try it right away.

I want users to be able to drag blocks onto a canvas, snap them together automatically, rearrange them, and remove them when needed. It should feel smooth and work on mobile too. Please make it minimal and easy to drop into a plain web app with just one script and one stylesheet, no big framework stuff. I also need a way to save the flowchart data and load it back later, plus a few hooks for when a block is grabbed, released, snapped, or moved around so I can connect it to my own app logic. Keep the design clean and polished, like a nice modern flowchart editor. If you need to check the latest browser behavior or docs for anything, look it up online first.