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/slidingstackedwidget.h

@@ -30,9 +30,13 @@ public:
     void setSpeed(int speed);
     void setEasingCurve(QEasingCurve::Type curveType);
 
-    
+
     void slideInIdx(int idx, SlideDirection direction = Automatic);
     void slideInWgt(QWidget *widget, SlideDirection direction = Automatic);
+    // Instant switch (no slide), safely finishing any in-flight animation.
+    // For targets with their own entrance animation (e.g. the player view).
+    void jumpToIdx(int idx);
+    void jumpToWgt(QWidget *widget);
     void disposeWidgetWhenSafe(QWidget *widget);
 
 Q_SIGNALS: