Fix supply voltage: apply PCB voltage dividers and read correct ADC source

Protocol Appendix A documents only the ADC reference voltage constant;
the PCB voltage divider must also be applied (from Thetis source):
- Boards 1-3 (Hermes/Angelia): ×(4.7+0.82)/0.82 ≈ 6.73, Vref=3.3V
- Board 5 (Orion MkII): ×(22+1)/1.1 ≈ 20.9, Vref=5.0V

For board type 5, supply voltage is measured via UserADC0 (bytes 57-58),
not the supply_volts field (bytes 49-50), matching Thetis behaviour.

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

HPSDRProtocol.pas

@@ -440,13 +440,17 @@ end;
 
 function ADCToSupplyVolts(RawADC: Word; BoardType: Integer): Double;
 begin
-  // Board 0 (Atlas) has no supply voltage measurement (protocol: "not Atlas bus systems")
-  // Boards 1,2,3 (Hermes/Angelia): V = ADC/4095 * 3.3  (Appendix A)
-  // Boards 4,5   (Orion):          V = ADC/4095 * 5.0  (Appendix A)
+  // Protocol Appendix A gives the ADC reference voltage only.
+  // The PCB voltage divider (from Thetis source) must also be applied.
+  // Board 0 (Atlas): no supply voltage measurement.
+  // Boards 1,2,3 (Hermes/Angelia): Vref=3.3V, PCB divider R1=4.7kΩ/R2=0.82kΩ.
+  // Board 5 (Orion MkII): Vref=5.0V, PCB divider R1=22kΩ/R2=1.1kΩ.
+  //   NOTE: for board 5 caller must pass UserADC0, not supply_volts bytes.
+  // Board 4 (Orion) and others: not available (return -1).
   case BoardType of
-    1, 2, 3: Result := (RawADC / 4095.0) * 3.3;
-    4, 5:    Result := (RawADC / 4095.0) * 5.0;
-  else       Result := -1.0;  // not documented or not applicable
+    1, 2, 3: Result := (RawADC / 4095.0) * 3.3 * ((4.7 + 0.82) / 0.82);
+    5:       Result := (RawADC / 4095.0) * 5.0 * ((22.0 + 1.0) / 1.1);
+  else       Result := -1.0;
   end;
 end;