XPL2 protocol foundation: wire framing, typed API, KA_PING, GS_JC_VERSION

Add Xpl2Protocol namespace with buildMessage/parseMessage for wire
serialization. Replace raw send/receive API on Xpl2Client with typed
protocol methods and internal dispatch. Auto-reply to KA_PING on all
sockets (qDebug only). Add GS_JC_VERSION as first typed command with
controllerId, firmwareVersion, hardwareVersion, printheadCount properties.

Upgrade mock server from echo to line-based command dispatch with 1s
KA_PING timer and canned GS_JC_VERSION response. Unknown commands
produce qWarning instead of echo.

Overhaul demo: remove raw send UI and port config, add wireDebug
toggle and Get JC Version button.

1 files changed, 27 insertions, 0 deletions

diff --git a/src/Xpl2Protocol.h b/src/Xpl2Protocol.h
new file mode 100644
index 0000000..6d4a348
--- /dev/null
+++ b/src/Xpl2Protocol.h
@@ -0,0 +1,27 @@
+/**
+ * @file   Xpl2Protocol.h
+ * @brief  Wire framing for the XPL2 printhead protocol.
+ */
+#pragma once
+
+#include <QByteArray>
+#include <QVariantList>
+
+namespace Xpl2Protocol
+{
+
+constexpr char Terminator = '\n';
+
+struct ParsedMessage
+{
+  QByteArray command;
+  QVariantList params;
+  bool valid = false;
+};
+
+QByteArray buildMessage (const QByteArray &command,
+                         const QVariantList &params = {});
+
+ParsedMessage parseMessage (const QByteArray &raw);
+
+} // namespace Xpl2Protocol