perf: smooth UI animations and reduce repaint overhead

Batch of performance and animation work: shared FadeHelper/MotionPrefs
primitives, hover animators, shadow pixmap caching, smooth scrolling,
seek time bubble, and widespread component repaint reductions.

src/qEmbyApp/components/moderncombobox.cpp

@@ -1,4 +1,6 @@
 #include "moderncombobox.h"
+#include "../utils/fadehelper.h"
+#include "../utils/popupfade.h"
 #include <QAbstractItemView>
 #include <QApplication>
 #include <QEvent>
@@ -132,6 +134,8 @@ void ModernComboBox::showPopup() {
     return;
   }
 
+  PopupFade::run(popupContainer);
+
   
   
   auto *vScrollBar = popupView->verticalScrollBar();
@@ -263,10 +267,12 @@ void ModernComboBox::showEmbeddedPopup() {
 
   listFrame->setGeometry(popupX, popupY, popupW, popupH);
 
-  
+
   overlay->show();
   overlay->raise();
   listFrame->show();
+  // Child overlay (not a top-level window) — FadeHelper, not PopupFade.
+  FadeHelper::fadeIn(listFrame, AnimationTokens::DurationMs::kQuick);
   listWidget->setFocus();