fix: handle removal of pending app items

1. Add check for pending app items in watchingAppItemRemoved
2. Handle cleanup of items in m_pendingAppItems container
3. Prevent potential memory leaks from unmanaged pending items
4. Ensure early return logic to avoid processing invalid active items
5. Improve app lifecycle management during installation or
initialization

Influence:
1. Test removing applications while they are in a pending state
2. Verify system stability when cancelling app installations
3. Check logs for "Removing pending app item" debug messages
4. Monitor for memory leaks during repeated app install/remove cycles
5. Ensure app icons disappear correctly after pending removal

PMS: BUG-347859

Author: caimc123456

src/ddeintegration/appmgr.cpp

@@ -532,6 +532,15 @@ void AppMgr::watchingAppItemAdded(const QString &key, AppItem *appItem)
 
 void AppMgr::watchingAppItemRemoved(const QString &key)
 {
+    // Check if the item is in pending container
+    if (m_pendingAppItems.contains(key)) {
+        auto pendingAppItem = m_pendingAppItems.value(key);
+        qCDebug(logDdeIntegration) << "Removing pending app item, desktopId" << pendingAppItem->id;
+        m_pendingAppItems.remove(key);
+        delete pendingAppItem;
+        return;
+    }
+    
     auto appItem = m_appItems.value(key);
     if (!appItem) {
         qCWarning(logDdeIntegration) << "App item not found for key:" << key;