Fix TX sequencing: PTT after Alex relay, SEQ error on startup

- Separate FPTTActive from FIsTransmitting so PTT bit in HP packet
  can be sent as a second packet after Alex bit27 (T/R relay) is set,
  matching Thetis behaviour: relay switches first, then PTT=1
- On TX stop: PTT=0 first, then Alex switches back to RX
- Add SendPTT(Active) method to THPSDRNetwork
- Reset FSeqHP to 0 in SetRunAndFreq(Run=True) to eliminate HP SEQ
  ERROR caused by intermediate SendFullHP calls before Run=1 packet
- RebuildXvtrButtons: use dynamic BtnH/RowH/MaxBottom instead of
  hardcoded px values so XVTR buttons scale correctly on HiDPI

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

HPSDRNetwork.pas

@@ -139,6 +139,7 @@ type
     FCurrentTXFreq:  Double;
     FCurrentDrive:   Byte;
     FIsTransmitting: Boolean;
+    FPTTActive:      Boolean;   // фактический PTT в HP-пакете (отдельно от Alex T/R)
     FPAEnabled:      Boolean;
     FAlexEnabled:    Boolean;
     FAlexConfig:     TAlexSettings;  // per-band antenna + routing config
@@ -215,6 +216,9 @@ type
     procedure SetXvtrMode(AEnable, AUseRxDDCIn, ADisablePA: Boolean;
                           ARxAnt: Byte);
     procedure SendFullHP;
+    // Отдельная отправка PTT: переключает реле (bit27) и drive ДО, потом PTT.
+    // Не меняет FIsTransmitting — вызывать после UpdateState+SendFullHP.
+    procedure SendPTT(Active: Boolean);
     procedure SendDDCAudio(const LeftRight: array of SmallInt);
     procedure SendDUCIQ(const IData, QData: array of Integer);
     procedure ClearDUCIQQueue;
@@ -946,13 +950,14 @@ begin
   FSocket := DoCreateSocket;
   if FSocket = SOCK_INVALID then Exit;
 
-  FConnected  := True;
-  FSeqGeneral := 0;
-  FSeqDDCSpec := 0;
-  FSeqDUCSpec := 0;
-  FSeqHP      := 0;
-  FSeqAudio   := 0;
-  FSeqDUCIQ   := 0;
+  FConnected      := True;
+  FPTTActive      := False;
+  FSeqGeneral     := 0;
+  FSeqDDCSpec     := 0;
+  FSeqDUCSpec     := 0;
+  FSeqHP          := 0;
+  FSeqAudio       := 0;
+  FSeqDUCIQ       := 0;
   ResetDUCIQQueue;
 
   StartThreads;
@@ -970,6 +975,7 @@ begin
   StopThreads;
   DoCloseSocket(FSocket);
   FConnected      := False;
+  FPTTActive      := False;
   FDevice.Valid   := False;
   FCachedDDCValid := False;
   FCachedDUCValid := False;
@@ -1365,7 +1371,7 @@ begin
   if FRunning then
   begin
     Buf[4] := HP_RUN;
-    if FIsTransmitting then Buf[4] := Buf[4] or HP_PTT0;
+    if FPTTActive then Buf[4] := Buf[4] or HP_PTT0;
   end;
 
   // DDC base: ORION/ORION2/ANGELIA/SATURN начинают с DDC2
@@ -1424,6 +1430,9 @@ end;
 procedure THPSDRNetwork.SetRunAndFreq(Run: Boolean; DDC0FreqHz, DUCFreqHz: Double;
                                       DriveLevel: Byte);
 begin
+  // При Run=1 аппаратура сбрасывает счётчик HP-последовательности.
+  // Синхронизируем свой счётчик чтобы не получить SEQ ERROR на первом пакете.
+  if Run then FSeqHP := 0;
   FRunning        := Run;
   FCurrentRXFreq  := DDC0FreqHz;
   FCurrentTXFreq  := DUCFreqHz;
@@ -1431,6 +1440,12 @@ begin
   SendFullHP;
 end;
 
+procedure THPSDRNetwork.SendPTT(Active: Boolean);
+begin
+  FPTTActive := Active;
+  if FConnected then SendFullHP;
+end;
+
 procedure THPSDRNetwork.SendDDCAudio(const LeftRight: array of SmallInt);
 var
   Pkt: TDDCAudioPacket;