Wire monitored property to OPC UA monitored items

The monitored bool now calls enableMonitoring/disableMonitoring on
the Value attribute. Adds publishingInterval property (default 100ms).
Value is no longer read at init — delivered by the monitored item.
Empty 4th demo page to verify monitoring stops when navigating away.

1 files changed, 18 insertions, 2 deletions

diff --git a/demo/NodePage.qml b/demo/NodePage.qml
index 442a6fd..a8e07d5 100644
--- a/demo/NodePage.qml
+++ b/demo/NodePage.qml
@@ -57,6 +57,12 @@ Page {
                 "ns=1;s=double_rw_array",
                 "ns=1;s=string_rw_array"
             ]
+        },
+        {
+            title: "Empty (Monitoring Test)",
+            description: "No nodes on this page. All previous pages are inactive,"
+                + " so the server log should show zero active monitored items.",
+            nodes: []
         }
     ]
 
@@ -78,7 +84,7 @@ Page {
                 font.pointSize: 14
             }
             Label {
-                text: "(" + nodePage.pageNumber + "/3)"
+                text: "(" + nodePage.pageNumber + "/" + nodePage.pages.length + ")"
                 color: "gray"
             }
             Item { Layout.fillWidth: true }
@@ -88,6 +94,16 @@ Page {
             }
         }
 
+        Label {
+            id: pageDescription
+            visible: currentPage.description !== undefined
+            text: currentPage.description || ""
+            wrapMode: Text.WordWrap
+            color: "gray"
+            font.italic: true
+            Layout.fillWidth: true
+        }
+
         // Column headers
         RowLayout {
             Layout.fillWidth: true
@@ -216,7 +232,7 @@ Page {
             Item { Layout.fillWidth: true }
             Button {
                 text: "Next →"
-                visible: nodePage.pageNumber < 3
+                visible: nodePage.pageNumber < nodePage.pages.length
                 onClicked: nodePage.stackRef.push("NodePage.qml", {
                     stackRef: nodePage.stackRef,
                     pageNumber: nodePage.pageNumber + 1,