When the tone-shift feature moves a tone into the model's 400-1200 Hz window,
the waterfall now shows two visual markers so the operator can see what is
happening: a green dashed line at the target (800 Hz) and an orange frequency
label at the top-left showing the original pitch.
The waterfall draws the RAW audio, not the shifted audio, so a 1500 Hz tone was
always invisible regardless of the shift setting. The markers close the gap:
the operator can now see that a tone was detected and where it was moved, even
when the original pitch is outside the visible band.
activeShiftHz is now a StateFlow exposed through ICwDecoder so the UI can
observe it without polling.
mckero
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