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>

Settings.pas

@@ -12,6 +12,11 @@ const
   SETTINGS_FILE  = 'hpsdr_settings.json';
   CFG_BAND_COUNT = 11;
   CFG_XVTR_COUNT = 8;     // количество XVTR-слотов (трансверторов)
+  // PA gain defaults (dB) — match Thetis HERMES/HPSDR defaults
+  // order: 160m,80m,60m,40m,30m,20m,17m,15m,12m,10m,6m
+  CFG_PA_BAND_CAL_DEFAULT: array[0..CFG_BAND_COUNT-1] of Double = (
+    41.0, 41.2, 41.3, 41.3, 41.0, 40.5, 39.9, 38.8, 38.8, 38.8, 38.8);
+  CFG_VHF_CAL_DEFAULT = 56.2; // dB, default for all XVTR slots
   CFG_BAND_DEFAULT_FREQ: array[0..CFG_BAND_COUNT-1] of Double = (
     1900000, 3750000, 5357000, 7100000, 10125000,
     14200000, 18120000, 21200000, 24940000, 28500000, 50150000);
@@ -223,6 +228,7 @@ type
     // --- PA (Power Amplifier) settings ---
     PAMaxPower:        Double;   // максимальная выходная мощность, Вт (5..200)
     PABandCal:         array[0..CFG_BAND_COUNT-1] of Double; // калибровка на диапазон 38.8..100.0
+    VHFBandCal:        array[0..CFG_XVTR_COUNT-1] of Double; // калибровка для XVTR слотов 38.8..100.0
     // --- ADC settings ---
     DitherEnabled:     Boolean;   // DDC Specific byte 5 — уменьшает интермодуляцию
     RandomEnabled:     Boolean;   // DDC Specific byte 6 — рандомизация ADC
@@ -362,7 +368,8 @@ begin
   G.WfNFEnabled := False;
   G.SampleRate := 192000;
   G.PAMaxPower := 100.0;
-  for i := 0 to CFG_BAND_COUNT-1 do G.PABandCal[i] := 100.0;
+  for i := 0 to CFG_BAND_COUNT-1 do G.PABandCal[i] := CFG_PA_BAND_CAL_DEFAULT[i];
+  for i := 0 to CFG_XVTR_COUNT-1 do G.VHFBandCal[i] := CFG_VHF_CAL_DEFAULT;
   // Display defaults
   G.FFTSize      := 131072;
   G.WindowType   := 2;     // Hann
@@ -604,7 +611,9 @@ begin
   // PA settings
   G.PAMaxPower := JD(GObj,'pa_max_power',100.0);
   for i := 0 to CFG_BAND_COUNT-1 do
-    G.PABandCal[i] := JD(GObj,'pa_band_cal_'+IntToStr(i),100.0);
+    G.PABandCal[i] := JD(GObj,'pa_band_cal_'+IntToStr(i), CFG_PA_BAND_CAL_DEFAULT[i]);
+  for i := 0 to CFG_XVTR_COUNT-1 do
+    G.VHFBandCal[i] := JD(GObj,'vhf_cal_'+IntToStr(i), CFG_VHF_CAL_DEFAULT);
   // CAT serial settings
   for i := 0 to 3 do begin
     G.CATSerialEnabled[i]  := JB(GObj,'cat_serial_en_'+IntToStr(i), False);
@@ -688,6 +697,8 @@ begin
   JW(O,'pa_max_power',G.PAMaxPower);
   for i := 0 to CFG_BAND_COUNT-1 do
     JW(O,'pa_band_cal_'+IntToStr(i),G.PABandCal[i]);
+  for i := 0 to CFG_XVTR_COUNT-1 do
+    JW(O,'vhf_cal_'+IntToStr(i),G.VHFBandCal[i]);
   // CAT serial settings
   for i := 0 to 3 do begin
     JW(O,'cat_serial_en_'+IntToStr(i),   G.CATSerialEnabled[i]);