Phase 3 (batch 12): consolidate VFO B tuning into controller command

The "set VFO B" engine block was duplicated inline across three tune paths
(DoSpectrumClick, DoSpectrumDrag, FreqDispBChanged), each subtly different
(drag had no band-detect/ruler; click had no drive recalc).

- TRadioController.SetVfoB(Hz): always stores FVfoB; when B is the active
  VFO, retunes the receiver (DDC=VFO B, no CTUN, shift 0), HF band-detects
  (FCurrentBand + drive recalc -> Changed(rfBand)) and pushes to the radio;
  when B is inactive (split, listening on A) it only stores the freq for TX.
  Fires Changed(rfVfoB).
- OnControllerState(rfVfoB): renders FreqDispB and, when B active, the
  spectrum/ruler (deferred via FSpectrumDirty, matching the rfVfoA path).

The three call sites collapse to a single FController.SetVfoB(...) each;
FreqDispBChanged is now a one-liner. Behavior unified: click/FreqDispB drop
from sync DrawSpectrum to deferred (consistent with VFO A click-to-tune,
imperceptible); drag gains band-detect + ruler refresh; click gains drive
recalc on band change. Net -23 lines.

Left inline (not identical): DoWidebandClick VFO B (extra XVTR clamp +
wideband-specific render) and SyncWebFreq (uses SetRunAndFreq, the web/run
network path, not UpdateState+SendFullHP). Builds clean, links.

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

RadioController.pas

@@ -571,7 +571,31 @@ begin
 end;
 
 procedure TRadioController.SetVfoB(Hz: Double);
-begin FVfoB := Hz; Changed(rfVfoB); { TODO wiring } end;
+// VFO B всегда сохраняется. Если B активен — перестраиваем приёмник (DDC=VFO B,
+// без CTUN, сдвиг 0), детектим диапазон и толкаем в сеть. Если B неактивен
+// (split, слушаем A) — только сохраняем частоту (используется для TX).
+// Рендер FreqDispB/спектра — в UI через OnControllerState(rfVfoB).
+var BandIdx: Integer;
+begin
+  FVfoB := Hz;
+  if FActiveVfo = 1 then
+  begin
+    FCenterFreq := FVfoB;
+    if FWDSPReady and Assigned(FDSPEngine) then FDSPEngine.SetShift(0.0);
+    if FCurrentXvtr < 0 then
+    begin
+      BandIdx := FreqToBandIdx(FVfoB);
+      if (BandIdx >= 0) and (BandIdx <> FCurrentBand) then
+      begin
+        FCurrentBand := BandIdx;
+        FDriveLevel  := CalcDriveByte;
+        Changed(rfBand);
+      end;
+    end;
+    PushNetworkState;
+  end;
+  Changed(rfVfoB);
+end;
 
 procedure TRadioController.SetActiveVfo(Idx: Integer);
 begin FActiveVfo := Idx; Changed(rfActiveVfo); { TODO wiring: ActivateVfo } end;