Fix VfoOverlay FM mode: NFM/FM filters, deviation sync, button layout

- FM filter row now shows only NFM (11 kHz) and FM (16 kHz) matching MainForm
- OnModeFilterSelect updates FFMDeviation and FFilter index for FM mode
- Mode and filter button widths distributed evenly (proportional, not fixed BtnW)
- S-meter inset by extra 4 px on each side

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

MainForm.pas

@@ -5519,9 +5519,22 @@ begin
 end;
 
 procedure TMainForm.OnModeFilterSelect(Mode: Integer; FilterBW: Integer);
+var
+  Idx: Integer;
 begin
   FMode     := Mode;
   FFilterBW := FilterBW;
+  if Mode = MODE_FM then
+  begin
+    FFilter := FILT_FM_DEF;
+    for Idx := 0 to FILT_FM_COUNT - 1 do
+      if FILT_FM_BW[Idx] = FilterBW then
+      begin
+        FFilter      := Idx;
+        FFMDeviation := FILT_FM_DEV[Idx];
+        Break;
+      end;
+  end;
   if FWDSPReady then
   begin
     FDSPEngine.SetMode(FMode);