Add configurable VFO frequency range with GHz support

- Settings > Display: new "VFO Display" control to select max frequency
  range (999 MHz / 9.999 GHz / 99.999 GHz), persisted as freq_mhz_digits
- FreqDisplay: extend digit map [0..10] to support up to 11 digit positions;
  keyboard navigation adapts to MinMhzDigits dynamically
- MainForm/LayoutTopVfoBlock: VFO panel width scales automatically with
  selected digit count using dynamic text measurement
- Web VFO: fix broken HTML (class attr not closed before data-s — wheel and
  hover were completely non-functional); rewrite fmtVfo to use variable MHz
  digit count synced from server state; fix missing </span> for .vfo-hz
- WebServer: publish freq_mhz_digits in state JSON; updated from
  ApplyFreqMhzDigits so desktop and web stay in sync
- Fix Int32 overflow on frequencies above ~2.15 GHz: CATEngine.Pad V param
  Int64, FormatFreq/FormatFreqSV Mhz var Int64 (Mhz*1000000 overflowed)

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

SettingsForm.pas

@@ -36,6 +36,7 @@ type
   // TX-настройки целиком (любая правка → один callback с актуальной структурой)
   TOnTXSettingsChange = procedure(const T: TTXSettings) of object;
 
+  TOnFreqMhzDigitsChange = procedure(Digits: Integer) of object;
   TOnDisplayParamChange = procedure(FFTSize, WindowType, SpecDetector,
     SpecAvgMode: Integer; SpecAvgTimeMS: Double) of object;
   TOnWaterfallParamChange = procedure(WfDetector, WfAvgMode: Integer;
@@ -109,6 +110,7 @@ type
     FChkShowWaterfall:   TCheckBox;
     FCmbFPS:             TComboBox;
     FChkLightTheme:      TCheckBox;
+    FCmbFreqMhzDigits:   TComboBox;
 
     // ---- PA Settings tab controls ----
     FEdMaxPower:     TSpinEdit;
@@ -243,8 +245,9 @@ type
     FOnAudioInDevChange: TOnAudioInDevChange;
     FOnVisibilityChange: TOnVisibilityChange;
     FOnFPSChange:        TOnFPSChange;
-    FOnThemeChange:      TOnThemeChange;
-    FOnTXChange:         TOnTXSettingsChange;
+    FOnThemeChange:            TOnThemeChange;
+    FOnFreqMhzDigitsChange:    TOnFreqMhzDigitsChange;
+    FOnTXChange:               TOnTXSettingsChange;
 
     FLoading: Boolean;
 
@@ -298,6 +301,7 @@ type
     procedure OnVisibilityChkChange(Sender: TObject);
     procedure OnFPSCmbChange(Sender: TObject);
     procedure OnLightThemeChkChange(Sender: TObject);
+    procedure OnFreqMhzDigitsCmbChange(Sender: TObject);
     procedure OnMaxPowerChange(Sender: TObject);
     procedure OnBandCalChange(Sender: TObject);
     procedure OnCATSerialChange(Sender: TObject);
@@ -335,6 +339,7 @@ type
     procedure LoadVisibility(ShowSpectrum, ShowWaterfall: Boolean);
     procedure LoadFPS(FPS: Integer);
     procedure LoadLightTheme(ALight: Boolean);
+    procedure LoadFreqMhzDigits(Digits: Integer);
     procedure LoadPASettings(MaxPower: Double; const BandCal: array of Double);
     procedure LoadCATSettings(
       const SerEnabled: array of Boolean;
@@ -357,6 +362,7 @@ type
     property OnVisibilityChange: TOnVisibilityChange     read FOnVisibilityChange write FOnVisibilityChange;
     property OnFPSChange:        TOnFPSChange            read FOnFPSChange       write FOnFPSChange;
     property OnThemeChange:      TOnThemeChange          read FOnThemeChange     write FOnThemeChange;
+    property OnFreqMhzDigitsChange: TOnFreqMhzDigitsChange read FOnFreqMhzDigitsChange write FOnFreqMhzDigitsChange;
     property OnTXChange:         TOnTXSettingsChange     read FOnTXChange        write FOnTXChange;
   end;
 
@@ -783,6 +789,15 @@ begin
   FChkLightTheme.Font.Name := UI_FONT;
   FChkLightTheme.Font.Size := 9;
   FChkLightTheme.OnChange := OnLightThemeChkChange;
+
+  Grp := MakeGroupPanel(FPageDisplay, 'VFO Display', MARGIN, 378, 650, 92);
+
+  MakeLbl(Grp, 'Frequency range', PAD, R1 + 5, LW);
+  FCmbFreqMhzDigits := MakeCombo(Grp, CX, R1, 240, OnFreqMhzDigitsCmbChange);
+  FCmbFreqMhzDigits.Items.Add('up to 999 MHz  (3 digits)');
+  FCmbFreqMhzDigits.Items.Add('up to 9.999 GHz  (4 digits)');
+  FCmbFreqMhzDigits.Items.Add('up to 99.999 GHz  (5 digits)');
+  FCmbFreqMhzDigits.ItemIndex := 0;
 end;
 
 // ---------------------------------------------------------------------------
@@ -2014,6 +2029,23 @@ begin
   else            ApplyTheme(DarkTheme);
 end;
 
+procedure TSettingsForm.LoadFreqMhzDigits(Digits: Integer);
+begin
+  FLoading := True;
+  try
+    FCmbFreqMhzDigits.ItemIndex := EnsureRange(Digits - 3, 0, 2);
+  finally
+    FLoading := False;
+  end;
+end;
+
+procedure TSettingsForm.OnFreqMhzDigitsCmbChange(Sender: TObject);
+begin
+  if FLoading then Exit;
+  if Assigned(FOnFreqMhzDigitsChange) then
+    FOnFreqMhzDigitsChange(FCmbFreqMhzDigits.ItemIndex + 3);
+end;
+
 procedure TSettingsForm.LoadPASettings(MaxPower: Double;
   const BandCal: array of Double);
 var i, n: Integer;