Fix TX following active RX VFO instead of the TX selector

The TX VFO is chosen independently of the RX VFO via the TX-A/TX-B buttons
(FSplitTxB: False=A, True=B); UI highlights TX-A when not split. But the TX
frequency and TX overlay used FActiveVfo in the non-split branch, coupling
TX to the active RX VFO. Result: with RX on B and TX-A selected, the radio
still transmitted on B (TX overlay also drew on B).

Make the TX VFO depend solely on FSplitTxB in all three spots:
ActiveTXFreqHz and both TXVfoIndex assignments (live update + ApplyMOX).
Now RX=B / TX=A works as the UI indicates. Pre-existing bug, not a refactor
regression. Builds clean, links.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

RadioController.pas

@@ -392,9 +392,11 @@ end;
 
 function TRadioController.ActiveTXFreqHz: Double;
 begin
+  // TX-VFO задаётся ТОЛЬКО селектором FSplitTxB (UI: кнопки TX-A/TX-B),
+  // независимо от активного RX-VFO. Раньше при не-split TX ошибочно следовал
+  // за активным RX (TX-A горит, но передача шла на B при активном B).
   if FSplitTxB then Result := FVfoB
-  else if FActiveVfo = 0 then Result := FVfoA
-  else Result := FVfoB;
+  else Result := FVfoA;
   if FMode = MODE_FM then
     case FFMRptDir of
       RPT_MINUS: Result := Result - FFMRptOffsetHz;