move animation setup to finalizeStyles

- This commit fixed layout shifting in glider

src/ztabwidget.cpp

@@ -85,10 +85,6 @@ void ZTabWidget::setupGlider()
                             "  border-radius: 1px;"
                             "}");
     m_glider->hide(); // Hide initially until tabs are added
-
-    m_gliderAnimation = new QPropertyAnimation(m_glider, "pos");
-    m_gliderAnimation->setDuration(250);
-    m_gliderAnimation->setEasingCurve(QEasingCurve::OutCubic);
 }
 
 ZTab *ZTabWidget::addTab(QWidget *widget, const QString &label)
@@ -132,6 +128,9 @@ void ZTabWidget::finalizeStyles()
                 int targetX = tab->pos().x();
                 int targetY = tab->pos().y() + tab->size().height() - 2;
                 m_glider->move(targetX, targetY);
+                m_gliderAnimation = new QPropertyAnimation(m_glider, "pos");
+                m_gliderAnimation->setDuration(250);
+                m_gliderAnimation->setEasingCurve(QEasingCurve::OutCubic);
                 m_glider->show();
             }
         });
@@ -183,6 +182,9 @@ void ZTabWidget::animateGlider(int index)
         // targetTabPos.y() + targetTabSize.height() + 6; // Position at bottom
         targetTabPos.y() + targetTabSize.height() - 2; // Position at bottom
 
+    if (m_gliderAnimation == nullptr)
+        return;
+
     m_gliderAnimation->stop();
     m_gliderAnimation->setStartValue(m_glider->pos());
     m_gliderAnimation->setEndValue(QPoint(targetX, targetY));

src/ztabwidget.h

@@ -67,7 +67,7 @@ private:
     QStackedWidget *m_stackedWidget;
     QButtonGroup *m_buttonGroup;
     QWidget *m_glider;
-    QPropertyAnimation *m_gliderAnimation;
+    QPropertyAnimation *m_gliderAnimation = nullptr;
     QList<ZTab *> m_tabs;
     QList<QWidget *> m_widgets;
     int m_currentIndex;