增加预览页介绍信息显示

client/gui/main_window/MainWindow.h

@@ -30,6 +30,7 @@ class TimelineWidget;
 namespace gui {
 class BackgroundPropertySection;
 class EntityPropertySection;
+class EntityIntroPopup;
 }
 
 class MainWindow : public QMainWindow {
@@ -96,6 +97,7 @@ private:
     void applyTimelineFromProject();
     void refreshDopeSheet();
     void setPreviewRequested(bool preview);
+    void syncPreviewPlaybackBar();
 
     QStackedWidget* m_centerStack = nullptr;
     QWidget* m_pageWelcome = nullptr;
@@ -174,4 +176,9 @@ private:
     // 旧版 DopeSheet 已移除，这里保留占位便于后续扩展区间 UI（如自定义小部件）
     QTreeWidget* m_dopeTree = nullptr;
     QPushButton* m_btnDopeDeleteKey = nullptr;
+
+    gui::EntityIntroPopup* m_entityIntroPopup = nullptr;
+    QFrame* m_previewPlaybackBar = nullptr;
+    QToolButton* m_previewBtnPlay = nullptr;
+    QToolButton* m_previewBtnPause = nullptr;
 };