dock: coordinated resize animation via centralized reservedWidthAnimated

shell/services/DockState.qml

@@ -11,6 +11,19 @@ QtObject {
     // Bar, screen corners, etc. read this to adjust layout.
     property int reservedWidth: 0
 
+    // Animated version for smooth visual transitions.
+    // Consumers that need coordinated movement use this instead.
+    property int reservedWidthAnimated: 0
+
+    Behavior on reservedWidthAnimated {
+        NumberAnimation {
+            duration: 200
+            easing.type: Easing.InOutCubic
+        }
+    }
+
+    onReservedWidthChanged: reservedWidthAnimated = reservedWidth
+
     onModeChanged: {
         if (mode !== "pinned")
             reservedWidth = 0;