fix: optimize property dialog layout stretch handling

- Move stretch item management to showEvent
- Remove redundant stretch item before adding new one
- Fix potential memory leak by properly deleting old stretch item

This change ensures proper layout spacing in the property dialog and
prevents multiple stretch items from being added unintentionally.

Log:

src/plugins/common/dfmplugin-propertydialog/views/filepropertydialog.cpp

@@ -130,7 +130,6 @@ void FilePropertyDialog::createPermissionManagerWidget(const QUrl &url)
     QVBoxLayout *vlayout = qobject_cast<QVBoxLayout *>(scrollArea->widget()->layout());
     if (vlayout) {
         insertExtendedControl(vlayout->count(), permissionManagerWidget);
-        vlayout->addStretch();
     }
 }
 
@@ -314,6 +313,18 @@ void FilePropertyDialog::resizeEvent(QResizeEvent *event)
 void FilePropertyDialog::showEvent(QShowEvent *event)
 {
     DDialog::showEvent(event);
+
+    QVBoxLayout *vlayout = qobject_cast<QVBoxLayout *>(scrollArea->widget()->layout());
+    if (vlayout) {
+        if (vlayout->count() > 0) {
+            QLayoutItem *item = vlayout->itemAt(vlayout->count() - 1);
+            if (item && item->spacerItem()) {
+                vlayout->removeItem(item);
+                delete item;
+            }
+        }
+        vlayout->addStretch();
+    }
 }
 
 void FilePropertyDialog::closeEvent(QCloseEvent *event)