UIUX: add a slider to set animated QR frame-rate

With some low budget camera/SoC, the current frame-rate for displaying animated QR codes is too high and the camera/SoC cannot keep up with the speed.
It would be nice to have some slider to adjust the QR animation speed.

Start by locating the animated QR display code and any existing frame-rate or animation-speed setting. Trace how the current rate is selected, then verify that a user-adjustable slider changes the animation speed and remains usable with slower cameras or SoCs.

Written by the indexing model from the issue text.