Add custom log handler and expand demo node coverage

Replace default Qt message pattern with a custom handler that matches
open62541 server log format: timestamps with UTC offset, colored
type/category tags padded to 20 chars, and shortened category names.

Add sbyte, byte, datetime, guid, and bytestring node types to all
three demo pages. Add Guid type coercion to writeValue.

3 files changed, 94 insertions, 14 deletions

diff --git a/demo/NodePage.qml b/demo/NodePage.qml
index a8e07d5..e9ae236 100644
--- a/demo/NodePage.qml
+++ b/demo/NodePage.qml
@@ -25,7 +25,12 @@ Page {
                 "ns=1;s=uint64_rw_scalar",
                 "ns=1;s=float_rw_scalar",
                 "ns=1;s=double_rw_scalar",
-                "ns=1;s=string_rw_scalar"
+                "ns=1;s=string_rw_scalar",
+                "ns=1;s=sbyte_rw_scalar",
+                "ns=1;s=byte_rw_scalar",
+                "ns=1;s=datetime_rw_scalar",
+                "ns=1;s=guid_rw_scalar",
+                "ns=1;s=bytestring_rw_scalar"
             ]
         },
         {
@@ -40,7 +45,12 @@ Page {
                 "ns=1;s=uint64_ro_scalar",
                 "ns=1;s=float_ro_scalar",
                 "ns=1;s=double_ro_scalar",
-                "ns=1;s=string_ro_scalar"
+                "ns=1;s=string_ro_scalar",
+                "ns=1;s=sbyte_ro_scalar",
+                "ns=1;s=byte_ro_scalar",
+                "ns=1;s=datetime_ro_scalar",
+                "ns=1;s=guid_ro_scalar",
+                "ns=1;s=bytestring_ro_scalar"
             ]
         },
         {
@@ -55,7 +65,12 @@ Page {
                 "ns=1;s=uint64_rw_array",
                 "ns=1;s=float_rw_array",
                 "ns=1;s=double_rw_array",
-                "ns=1;s=string_rw_array"
+                "ns=1;s=string_rw_array",
+                "ns=1;s=sbyte_rw_array",
+                "ns=1;s=byte_rw_array",
+                "ns=1;s=datetime_rw_array",
+                "ns=1;s=guid_rw_array",
+                "ns=1;s=bytestring_rw_array"
             ]
         },
         {
diff --git a/demo/main.cpp b/demo/main.cpp
index 6d0b9be..689b998 100644
--- a/demo/main.cpp
+++ b/demo/main.cpp
@@ -2,24 +2,83 @@
  * @file   main.cpp
  * @brief  Entry point for the Bobink demo application.
  */
+#include <QDateTime>
 #include <QGuiApplication>
 #include <QQmlApplicationEngine>
 
 #include <QtQml/QQmlExtensionPlugin>
-Q_IMPORT_QML_PLUGIN(BobinkPlugin)
+Q_IMPORT_QML_PLUGIN (BobinkPlugin)
 
-int main(int argc, char *argv[])
+/** @brief Custom log handler matching open62541 server log format. */
+static void
+logHandler (QtMsgType type, const QMessageLogContext &ctx, const QString &msg)
 {
-    // Load the locally-built OpcUa backend plugin (open62541).
-    QCoreApplication::addLibraryPath(QStringLiteral(QTOPCUA_PLUGIN_PATH));
+  // Color only the type/category tag.
+  const char *color = "";
+  const char *label = "debug";
+  switch (type)
+    {
+    case QtDebugMsg:
+      label = "debug";
+      break;
+    case QtInfoMsg:
+      color = "\x1b[32m";
+      label = "info";
+      break;
+    case QtWarningMsg:
+      color = "\x1b[33m";
+      label = "warning";
+      break;
+    case QtCriticalMsg:
+      color = "\x1b[31m";
+      label = "critical";
+      break;
+    case QtFatalMsg:
+      color = "\x1b[1;31m";
+      label = "fatal";
+      break;
+    }
 
-    QGuiApplication app(argc, argv);
+  // Shorten "qt.opcua.plugins.open62541.sdk.client" → "client".
+  QLatin1StringView cat (ctx.category ? ctx.category : "default");
+  qsizetype dot = cat.lastIndexOf (QLatin1Char ('.'));
+  if (dot >= 0)
+    cat = cat.sliced (dot + 1);
 
-    QQmlApplicationEngine engine;
-    QObject::connect (
-        &engine, &QQmlApplicationEngine::objectCreationFailed, &app,
-        [] () { QCoreApplication::exit (1); }, Qt::QueuedConnection);
+  // "debug/client", "warning/network", etc. — padded to 20 chars.
+  QByteArray tag
+      = QByteArray (label) + '/' + QByteArray (cat.data (), cat.size ());
 
-    engine.loadFromModule("BobinkDemo", "Main");
-    return app.exec();
+  // Format UTC offset as "(UTC+0100)" to match open62541 server logs.
+  QDateTime now = QDateTime::currentDateTime ();
+  qint32 offset = now.offsetFromUtc ();
+  QChar sign = offset >= 0 ? u'+' : u'-';
+  offset = qAbs (offset);
+  QString ts = now.toString (u"yyyy-MM-dd HH:mm:ss.zzz")
+               + QStringLiteral (" (UTC%1%2%3)")
+                     .arg (sign)
+                     .arg (offset / 3600, 2, 10, QLatin1Char ('0'))
+                     .arg ((offset % 3600) / 60, 2, 10, QLatin1Char ('0'));
+
+  fprintf (stderr, "[%s] %s%-20.*s\x1b[0m %s\n", qPrintable (ts), color,
+           static_cast<int> (tag.size ()), tag.data (), qPrintable (msg));
+}
+
+int
+main (int argc, char *argv[])
+{
+  // Load the locally-built OpcUa backend plugin (open62541).
+  QCoreApplication::addLibraryPath (QStringLiteral (QTOPCUA_PLUGIN_PATH));
+
+  qInstallMessageHandler (logHandler);
+
+  QGuiApplication app (argc, argv);
+
+  QQmlApplicationEngine engine;
+  QObject::connect (
+      &engine, &QQmlApplicationEngine::objectCreationFailed, &app,
+      [] () { QCoreApplication::exit (1); }, Qt::QueuedConnection);
+
+  engine.loadFromModule ("BobinkDemo", "Main");
+  return app.exec ();
 }
diff --git a/src/OpcUaMonitoredNode.cpp b/src/OpcUaMonitoredNode.cpp
index 1a2da86..cd93730 100644
--- a/src/OpcUaMonitoredNode.cpp
+++ b/src/OpcUaMonitoredNode.cpp
@@ -9,6 +9,7 @@
 #include <QOpcUaLocalizedText>
 #include <QOpcUaMonitoringParameters>
 #include <QStringList>
+#include <QUuid>
 
 OpcUaMonitoredNode::OpcUaMonitoredNode (QObject *parent) : QObject (parent) {}
 
@@ -451,6 +452,11 @@ OpcUaMonitoredNode::coerceValue (const QVariant &input) const
       }
     case QOpcUa::ByteString:
       return QVariant::fromValue (input.toByteArray ());
+    case QOpcUa::Guid:
+      {
+        QUuid uuid (input.toString ());
+        return !uuid.isNull () ? QVariant::fromValue (uuid) : QVariant{};
+      }
     default:
       return input;
     }