Hey this is pretty cool. Instead of Electron app I would prefer it as a browser tab. Wish it could be self hosted.
You can use the web version, it's all offline and saved in localStorage. Works well in mobile too and can be "installed" as an app from there.
If you wanna see this in a little executable that you can pass around to your friends, check out this repo I threw up: https://github.com/shmup/redbean-calcpad
This is now essentially an offline CalcPad that still leverages LocalStorage, since the UI is your browser. I've configured this specific build to automatically launch your default browser when you run it.