Show Igor battery voltage in Mobile IO

[Daniiiil1]

Summary

Implements the battery-voltage UI part of #130 for the Igor 2 demo.

Changes

• average finite supply-voltage feedback across the Igor module group
• display the value on Mobile IO as Battery: XX.X V
• refresh at most once per second and only after a meaningful 0.1 V change
• force an initial update after the run layout is loaded
• use non-blocking Mobile IO writes so a disconnected tablet cannot stall the balance-control loop

Validation

• python3 -m compileall -q kits/igor2
• git diff --check

Hardware-in-the-loop validation requires an Igor and Mobile IO device and was not available locally.

This intentionally leaves the trajectory-smoothing part of #130 for a separate change.