peetzweg/opendisplay ? reverse-engineered prompt

Build me a free, open source app that lets my iPhone or iPad work as a real second monitor for my Mac, not just screen mirroring.

I want it to connect over WiFi or a USB cable, with a simple way to pick the device from the Mac and have it show up like a proper extended display in macOS. The image should look sharp on Retina screens, feel low latency, and support touch input so I can tap to click, drag windows, and scroll with two fingers. If possible, also let me use a spare Mac as the receiver so another Mac can act like the second monitor too.

Please make the whole experience feel polished and easy to set up, with the sender and receiver apps working together cleanly. If you need to check current Apple docs or APIs while building it, go ahead and look them up online.