fashionfreedom/seamly2d ? reverse-engineered prompt

Build me a desktop app for making sewing patterns that feels friendly for people who want to design their own clothes. I want it to let someone enter either standard size measurements or their own custom measurements, then use those measurements to create and edit 2D garment patterns on screen. It should work on Windows, Mac, and Linux, and have a clean Qt based interface that feels like a real desktop tool, not a web app.

Please make the main flow easy to understand, with a canvas for drawing and adjusting pattern pieces, basic tools for viewing and editing measurements, and a way to save and reopen projects. If there are any good patternmaking or geometry docs you need, look them up online first. Keep it open source friendly and make the app feel polished enough that a home sewer could actually use it without needing to be technical.