Add VHF XVTR PA calibration; fix TX drive formula and stale FDriveLevel

PA calibration per band (HF and VHF):
- Add VHFBandCal[0..7] in TGlobalSettings (saved as vhf_cal_0..7 in JSON)
- Default HF cal updated to Thetis HERMES defaults (38.8-41.3 dB per band)
- Default VHF cal = 56.2 dB (Thetis HERMES XVTR default)
- SettingsForm: second group in PA tab "VHF Calibration (Transverters)" with
  8 spinboxes VHF0..VHF7; labels dynamically show XVTR slot ButtonText
  when LoadXvtrSettings is called (e.g. "VHF0 (2m):")

TX drive formula (CalcDriveByte) rewritten to match Thetis exactly:
  drive_byte = min(sqrt(10^((10*log10(pwr_W*1000) - Cal)/10) * 0.05) / 0.8, 1.0) * 1.02 * 255
  Cal = PA gain in dB (not a percentage); matches Thetis verified output
  (Cal=63.1 + slider=100% + PAMax=100W → drive_byte=16, verified against Thetis)
  Old formula Pos/100*Cal/100*255 was wrong: treated dB gain as linear percent

Fix stale FDriveLevel not updated on band/XVTR switch:
- Startup: FCurrentBand must be set before CalcDriveByte (was reversed)
- RestoreBand: recalculate FDriveLevel before ApplyVfoA network update
- ActivateXvtrBand: recalculate after FCurrentXvtr changes
- ApplyVfoA: recalculate when VFO crosses HF band boundary
- FreqDispBChanged: same for VFO-B band changes
- ApplyMOX(True): safety recalculate at PTT engage time

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SettingsForm.pas

@@ -33,6 +33,8 @@ type
   // PA: MaxPower в Вт, BandCal[0..10] — калибровка 38.8..100.0 на диапазон
   TOnPASettingsChange = procedure(MaxPower: Double;
                                   const BandCal: array of Double) of object;
+  // VHF (XVTR) PA calibration: 8 slots, 38.8..100.0
+  TOnVHFCalChange = procedure(const VHFCal: array of Double) of object;
   // TX-настройки целиком (любая правка → один callback с актуальной структурой)
   TOnTXSettingsChange = procedure(const T: TTXSettings) of object;
 
@@ -121,6 +123,8 @@ type
     // ---- PA Settings tab controls ----
     FEdMaxPower:     TSpinEdit;
     FEdBandCal:      array[0..10] of TFloatSpinEdit;
+    FEdVHFCal:       array[0..CFG_XVTR_COUNT-1] of TFloatSpinEdit;
+    FVHFCalLabels:   array[0..CFG_XVTR_COUNT-1] of TLabel;
 
     // ---- Transmit tab controls ----
     // Текущее состояние, отдаётся в OnTXChange целиком при любой правке.
@@ -252,6 +256,7 @@ type
     // ---- Callbacks ----
     FOnCATChange:        TOnCATChange;
     FOnPAChange:         TOnPASettingsChange;
+    FOnVHFCalChange:     TOnVHFCalChange;
     FOnADCChange:        TOnADCChange;
     FOnWebSettingsChange: TOnWebSettingsChange;
     FOnDisplayChange:    TOnDisplayParamChange;
@@ -325,6 +330,7 @@ type
     procedure OnFreqMhzDigitsCmbChange(Sender: TObject);
     procedure OnMaxPowerChange(Sender: TObject);
     procedure OnBandCalChange(Sender: TObject);
+    procedure OnVHFCalEdit(Sender: TObject);
     procedure OnCATSerialChange(Sender: TObject);
     procedure OnCATTcpChange(Sender: TObject);
     procedure FireCATChange;
@@ -362,6 +368,7 @@ type
     procedure LoadLightTheme(ALight: Boolean);
     procedure LoadFreqMhzDigits(Digits: Integer);
     procedure LoadPASettings(MaxPower: Double; const BandCal: array of Double);
+    procedure LoadVHFCalSettings(const VHFCal: array of Double);
     procedure LoadCATSettings(
       const SerEnabled: array of Boolean;
       const SerPort: array of string;
@@ -379,6 +386,7 @@ type
     property OnAlexChange:       TOnAlexChange           read FOnAlexChange      write FOnAlexChange;
     property OnXvtrChange:       TOnXvtrChange           read FOnXvtrChange      write FOnXvtrChange;
     property OnPAChange:         TOnPASettingsChange     read FOnPAChange        write FOnPAChange;
+    property OnVHFCalChange:     TOnVHFCalChange         read FOnVHFCalChange    write FOnVHFCalChange;
     property OnDisplayChange:    TOnDisplayParamChange   read FOnDisplayChange   write FOnDisplayChange;
     property OnWaterfallChange:  TOnWaterfallParamChange read FOnWaterfallChange write FOnWaterfallChange;
     property OnGridChange:       TOnGridParamChange      read FOnGridChange      write FOnGridChange;
@@ -1584,6 +1592,38 @@ begin
     FEdBandCal[i].Tag := i;
   end;
 
+  // ── VHF Calibration (Transverters) ──────────────────────────────────────
+  Grp := MakeGroupPanel(FPagePA, 'VHF Calibration (Transverters)',
+                        MARGIN, 86 + GRP_H + 14, 650, 2 * ROW_H + 62);
+
+  Lbl            := TLabel.Create(Self);
+  Lbl.Parent     := Grp;
+  Lbl.Caption    := 'Calibration per transverter slot, 38.8 ... 100.0';
+  Lbl.SetBounds(GRP_PAD, 16, 400, 18);
+  Lbl.Font.Color := CLR_TEXTDIM;
+  Lbl.Font.Name  := UI_FONT;
+  Lbl.Font.Size  := 9;
+
+  for i := 0 to CFG_XVTR_COUNT - 1 do
+  begin
+    r := i div COLS;
+    c := i mod COLS;
+    X := GRP_PAD + c * (COL_W + 4);
+    Y := 38 + r * ROW_H;
+
+    Lbl            := TLabel.Create(Self);
+    Lbl.Parent     := Grp;
+    Lbl.Caption    := 'VHF' + IntToStr(i) + ':';
+    Lbl.SetBounds(X, Y + 5, LBL_W, 18);
+    Lbl.Font.Color := CLR_TEXTDIM;
+    Lbl.Font.Name  := UI_FONT;
+    Lbl.Font.Size  := 9;
+    FVHFCalLabels[i] := Lbl;
+
+    FEdVHFCal[i]     := MakeFloatSpin(Grp, X + LBL_W, Y, OnVHFCalEdit);
+    FEdVHFCal[i].Tag := i;
+  end;
+
 end;
 
 procedure TSettingsForm.BuildAdvancedTab;
@@ -2299,6 +2339,31 @@ begin
   FOnPAChange(FEdMaxPower.Value, BandCal);
 end;
 
+procedure TSettingsForm.LoadVHFCalSettings(const VHFCal: array of Double);
+var i, n: Integer;
+begin
+  FLoading := True;
+  try
+    n := Min(CFG_XVTR_COUNT - 1, High(VHFCal));
+    for i := 0 to n do
+      FEdVHFCal[i].Value := EnsureRange(VHFCal[i], 38.8, 100.0);
+  finally
+    FLoading := False;
+  end;
+end;
+
+procedure TSettingsForm.OnVHFCalEdit(Sender: TObject);
+var
+  VHFCal: array[0..CFG_XVTR_COUNT-1] of Double;
+  i: Integer;
+begin
+  if FLoading then Exit;
+  if not Assigned(FOnVHFCalChange) then Exit;
+  for i := 0 to CFG_XVTR_COUNT - 1 do
+    VHFCal[i] := FEdVHFCal[i].Value;
+  FOnVHFCalChange(VHFCal);
+end;
+
 procedure TSettingsForm.BtnCloseClick(Sender: TObject);
 begin
   Close;
@@ -3106,6 +3171,14 @@ begin
       if FXvtrRXAnt[i] <> nil then
         FXvtrRXAnt[i].ItemIndex := EnsureRange(X.Entries[i].RXAntenna, 0, 3);
       UpdateXvtrRowEnabled(i);
+      // Sync VHF calibration label in PA tab
+      if FVHFCalLabels[i] <> nil then
+      begin
+        if X.Entries[i].ButtonText <> '' then
+          FVHFCalLabels[i].Caption := 'VHF' + IntToStr(i) + ' (' + X.Entries[i].ButtonText + '):'
+        else
+          FVHFCalLabels[i].Caption := 'VHF' + IntToStr(i) + ':';
+      end;
     end;
     if FChkXvtrTunPwr <> nil then FChkXvtrTunPwr.Checked := X.UseXVTRTunePower;
   finally