`AudioLevelMeter` measured one number for everything. It now also keeps smoothed per-channel
levels with the same attack/decay, plus `ImbalanceDb`. Mono samples report both sides equal (a mono
source is centred), so the two never disagree about whether audio exists.
The dock shows ONE ladder per source — two ladders per bay was visual noise for a rare failure —
but this creator is profoundly deaf on the right, so the one case that matters is "the sound is
panned away from me". That is now measurable and will drive a flag, not a second ladder.
Semantics that mattered: a silent side is compared at the −60 dBFS floor, so a fully one-sided
signal reads ≈54 dB rather than "nothing to compare". My first version returned 0 for exactly the
case the feature exists for; the test caught it.
Guard: StereoMeterTests — hard left, hard right (the inaudible case), balanced stereo, mono
centred, and silence-is-not-an-imbalance. 31 audio tests green.
