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/views/settings/settingsview.cpp

@@ -1,4 +1,6 @@
 #include "settingsview.h"
+#include "../../tokens/AnimationTokens.h"
+#include "../../utils/motionprefs.h"
 #include "../../components/slidingstackedwidget.h"
 #include "../../managers/thememanager.h" 
 #include "pageabout.h"
@@ -148,8 +150,8 @@ QScrollArea *SettingsView::wrapInScrollArea(QWidget *page, int row) {
 
     auto *anim =
         new QPropertyAnimation(scroll->verticalScrollBar(), "value", this);
-    anim->setEasingCurve(QEasingCurve::OutCubic);
-    anim->setDuration(450);
+    anim->setEasingCurve(AnimationTokens::Curve::enter());
+    anim->setDuration(AnimationTokens::DurationMs::kSlow);
     m_scrollAnims[row] = anim;
     m_scrollTargets[row] = 0;
   }
@@ -195,10 +197,10 @@ void SettingsView::ensurePageAt(int row) {
   
   QWidget *placeholder = m_stack->widget(row);
   const bool wasBlocked = m_stack->blockSignals(true);
-  m_stack->insertWidget(row, scroll); 
+  m_stack->insertWidget(row, scroll);
   m_stack->removeWidget(placeholder);
   m_stack->blockSignals(wasBlocked);
-  placeholder->deleteLater();
+  m_stack->disposeWidgetWhenSafe(placeholder);
 
   m_pages[row] = scroll;
 }
@@ -208,7 +210,10 @@ void SettingsView::setupConnections() {
   connect(m_navMenu, &QListWidget::currentRowChanged, this, [this](int row) {
     if (row >= 0) {
       ensurePageAt(row);
-      m_stack->setCurrentIndex(row);
+      // Vertical slide following the nav list's direction of travel.
+      m_stack->slideInIdx(row, row > m_stack->currentIndex()
+                                   ? SlidingStackedWidget::BottomToTop
+                                   : SlidingStackedWidget::TopToBottom);
     }
   });
 
@@ -261,9 +266,13 @@ bool SettingsView::eventFilter(QObject *obj, QEvent *event) {
           if (newTarget != vBar->value()) {
             m_scrollTargets[i] = newTarget;
             anim->stop();
-            anim->setStartValue(vBar->value());
-            anim->setEndValue(newTarget);
-            anim->start();
+            if (MotionPrefs::reduceMotion()) {
+              vBar->setValue(newTarget);
+            } else {
+              anim->setStartValue(vBar->value());
+              anim->setEndValue(newTarget);
+              anim->start();
+            }
           }
         }
         return true;