peterklingelhofer/exhale ? reverse-engineered prompt

Build me a simple cross platform breathing app that sits on top of other windows as a translucent overlay and gently expands and contracts to guide breathing.

I want it to feel calm and minimal, with a small settings panel where I can choose the inhale, hold, exhale, and pause timing, plus adjust things like size, shape, and opacity. It should have a tray or menu bar icon, start, stop, reset, and quit controls, and a preferences shortcut. I also want keyboard shortcuts I can customize, with only the preferences one set by default so it does not clash with other apps.

Please make it work on Mac, Windows, and Linux, and keep it lightweight so it does not eat CPU when idle. If you need to look up current docs online while building it, go ahead. Also include a short disclaimer that it is for general wellness and not medical advice.