Phase 3 (batch 17): move CTUN center scroll (SetCenter) into the controller

SetCenter was a Phase-1 skeleton; filled it with the CTUN view-scroll
logic: set FCenterFreq, shift the demodulator by (active VFO - center),
push a full HP frame, and emit Changed(rfCenterFreq). The UI renders via
OnControllerState (invalidate ruler cache + deferred spectrum redraw, since
a drag emits many events).

Both entry points now call FController.SetCenter: the desktop CTUN drag
(DoSpectrumDrag) and the web center scroll (SyncWebCenter). Removes the
duplicated inline shift/network logic from both.

Side effect / latent fix: the web center scroll previously only called
UpdateState without SendFullHP (the desktop path did both), so a web scroll
did not push the new DDC center to the radio immediately. Routing it through
PushNetworkState now sends the full HP frame like the desktop path.

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

RadioController.pas

@@ -893,7 +893,17 @@ begin
 end;
 
 procedure TRadioController.SetCenter(Hz: Double);
-begin FCenterFreq := Hz; Changed(rfCenterFreq); { TODO wiring } end;
+// CTUN-скролл окна просмотра: двигаем DDC-центр БЕЗ смены VFO. Демодулятор
+// сдвигаем = активный VFO − новый центр; полный HP-кадр в радио. Рендер
+// (ruler/спектр) — в UI через OnControllerState(rfCenterFreq).
+// Точки входа: десктопный CTUN-drag и web (SyncWebCenter).
+begin
+  FCenterFreq := Hz;
+  if FWDSPReady and Assigned(FDSPEngine) then
+    FDSPEngine.SetShift(ActiveVfoHz - FCenterFreq);
+  PushNetworkState;
+  Changed(rfCenterFreq);
+end;
 
 procedure TRadioController.VfoSwap;
 // Меняем VFO A/B местами и перестраиваем приёмник на новую частоту активного