Microphone Warning Behavior and Input Detection Improvements

We fixed an issue where the low-audio warning message could briefly persist after switching to a different microphone, even when valid audio input was present. The warning now clears correctly when changing devices.

We adopted a universally accepted RMS (root mean square) calculation for measuring the microphone input level. We also set the threshold for showing a warning message to below the room-silence level based on 30+ tests with different microphone devices. The threshold is 0.00002.

Build slug: a21aea38f