diagrams: Meta+click-drag to pan fullscreen viewer

Left-click drag was unreliable for panning. Use Meta (Super/Win key)
+ left-click-drag instead. Flickable interactive mode disabled;
panning is handled manually via MouseArea.

gui/ChatPane.qml

@@ -1469,6 +1469,7 @@ Item {
             contentWidth: diagramZoomImg.width
             contentHeight: diagramZoomImg.height
             boundsBehavior: Flickable.StopAtBounds
+            interactive: false  // disable default drag — we handle it via Meta+drag
 
             Image {
                 id: diagramZoomImg
@@ -1485,6 +1486,31 @@ Item {
             MouseArea {
                 anchors.fill: parent
                 acceptedButtons: Qt.LeftButton | Qt.RightButton
+                property real startX: 0
+                property real startY: 0
+                property real startContentX: 0
+                property real startContentY: 0
+                property bool panning: false
+
+                onPressed: function(mouse) {
+                    if (mouse.button === Qt.LeftButton && (mouse.modifiers & Qt.MetaModifier)) {
+                        panning = true
+                        startX = mouse.x
+                        startY = mouse.y
+                        startContentX = diagramFlick.contentX
+                        startContentY = diagramFlick.contentY
+                        mouse.accepted = true
+                    }
+                }
+                onPositionChanged: function(mouse) {
+                    if (panning) {
+                        diagramFlick.contentX = Math.max(0, Math.min(diagramFlick.contentWidth - diagramFlick.width, startContentX - (mouse.x - startX)))
+                        diagramFlick.contentY = Math.max(0, Math.min(diagramFlick.contentHeight - diagramFlick.height, startContentY - (mouse.y - startY)))
+                    }
+                }
+                onReleased: function(mouse) {
+                    panning = false
+                }
                 onClicked: function(mouse) {
                     if (mouse.button === Qt.RightButton)
                         diagramFullscreen.close()

gui/main-kf5.qml

@@ -2279,6 +2279,7 @@ ApplicationWindow {
             contentWidth: diagramZoomImg.width
             contentHeight: diagramZoomImg.height
             boundsBehavior: Flickable.StopAtBounds
+            interactive: false  // disable default drag — we handle it via Meta+drag
 
             Image {
                 id: diagramZoomImg
@@ -2294,6 +2295,31 @@ ApplicationWindow {
             MouseArea {
                 anchors.fill: parent
                 acceptedButtons: Qt.LeftButton | Qt.RightButton
+                property real startX: 0
+                property real startY: 0
+                property real startContentX: 0
+                property real startContentY: 0
+                property bool panning: false
+
+                onPressed: function(mouse) {
+                    if (mouse.button === Qt.LeftButton && (mouse.modifiers & Qt.MetaModifier)) {
+                        panning = true
+                        startX = mouse.x
+                        startY = mouse.y
+                        startContentX = diagramFlick.contentX
+                        startContentY = diagramFlick.contentY
+                        mouse.accepted = true
+                    }
+                }
+                onPositionChanged: function(mouse) {
+                    if (panning) {
+                        diagramFlick.contentX = Math.max(0, Math.min(diagramFlick.contentWidth - diagramFlick.width, startContentX - (mouse.x - startX)))
+                        diagramFlick.contentY = Math.max(0, Math.min(diagramFlick.contentHeight - diagramFlick.height, startContentY - (mouse.y - startY)))
+                    }
+                }
+                onReleased: function(mouse) {
+                    panning = false
+                }
                 onClicked: function(mouse) {
                     if (mouse.button === Qt.RightButton)
                         diagramFullscreen.close()