One-click PEA toggle

Add a switch that applies pulseless electrical activity to whatever rhythm is currently selected, instead of PEA only existing as its own separate preset. In real life PEA means the heart's electrical signal looks normal but there is no effective pumping, so the actual training goal is teaching students to check for a pulse even when the monitor looks fine.

We tested this on a competitor app. Turning the switch on kept the ECG exactly the same, since the rhythm itself does not change. SpO2 went flat, since there is no real blood flow for the pulse oximeter to detect. EtCO2 dropped a bit but not to zero, since less blood is circulating to carry carbon dioxide back to the lungs.

For our version, the rule should be that this switch only affects SpO2 and EtCO2, and never touches the ECG rendering. That is the detail that keeps this teaching the right lesson. Right now we do not have any way to trigger PEA in our controller at all, there is leftover code for it but nothing in the interface actually uses it.