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/utils/shadowpixmap.cpp

@@ -105,4 +105,41 @@ NinePatchShadow make(int blurRadius, int cornerRadius, const QColor &color, qrea
     baked.save(path, "PNG"); // best-effort cache; failure just re-bakes next time
     return result;
 }
+
+void drawNinePatch(QPainter *painter, const QRect &target, const NinePatchShadow &patch)
+{
+    if (!painter || patch.isNull())
+    {
+        return;
+    }
+
+    const int b = patch.border;
+    const int t = patch.total;
+    const qreal s = patch.dpr;
+    const QRect r = target;
+
+    // Degenerate target (smaller than the two fixed borders): nothing sensible
+    // to slice, skip rather than draw garbage.
+    if (r.width() < 2 * b || r.height() < 2 * b)
+    {
+        return;
+    }
+
+    // 3x3 grid: corners fixed, edges/centre stretched. Target columns/rows are
+    // logical; source columns/rows are physical (pixmap carries no dpr).
+    const int xt[4] = {r.left(), r.left() + b, r.right() + 1 - b, r.right() + 1};
+    const int yt[4] = {r.top(), r.top() + b, r.bottom() + 1 - b, r.bottom() + 1};
+    const qreal xs[4] = {0.0, b * s, (t - b) * s, t * s};
+    const qreal ys[4] = {0.0, b * s, (t - b) * s, t * s};
+
+    for (int i = 0; i < 3; ++i)
+    {
+        for (int j = 0; j < 3; ++j)
+        {
+            const QRectF targetCell(xt[i], yt[j], xt[i + 1] - xt[i], yt[j + 1] - yt[j]);
+            const QRectF sourceCell(xs[i], ys[j], xs[i + 1] - xs[i], ys[j + 1] - ys[j]);
+            painter->drawPixmap(targetCell, patch.pixmap, sourceCell);
+        }
+    }
+}
 } // namespace ShadowPixmap