alexpcosta/opengym ? reverse-engineered prompt

Build me a self hosted gym and body weight tracker that runs in the browser and works nicely on phone and desktop.

I want to be able to set up a weekly workout plan, open today’s session, and log sets as I go, including supersets, timed exercises like planks, and cardio. It should remember my last weights, show a rest timer, track progress over time, and let me enter body weight with a chart and goal line. I also want a simple stats area with PRs, training history, and a heatmap style view of activity.

Make it feel like a real app, with offline support, installable like a PWA, passkey login, and syncing across devices for each profile. Add the ability to share or import a plan file and print a clean PDF. If it makes sense, include an optional AI coach that can suggest a training plan and adjust it based on what I actually log, but only after I approve changes. Please look up current docs online if you need to.