refactor: Uses single QML engine for all QML code (#323)

* refactor: Uses single QML engine for all QML code

* fix: Adds missing `QPointer` include

* Parents QML engine instance to plugin instance.

---------

Co-authored-by: Ivan Lebedev <ilebedev@flightpath3d.com>
Co-authored-by: Ivan Lebedev <ilebedev1988@gmail.com>

chat/NavigationPanel.cpp

@@ -7,7 +7,8 @@
 
 namespace QodeAssist::Chat {
 
-NavigationPanel::NavigationPanel()
+NavigationPanel::NavigationPanel(QQmlEngine* engine)
+    : m_engine{engine}
 {
     setDisplayName(tr("QodeAssist Chat"));
     setPriority(500);
@@ -19,10 +20,7 @@ NavigationPanel::~NavigationPanel() {}
 
 Core::NavigationView NavigationPanel::createWidget()
 {
-    Core::NavigationView view;
-    view.widget = new ChatWidget;
-
-    return view;
+    return {.widget = new ChatWidget{m_engine}};
 }
 
 } // namespace QodeAssist::Chat