Optimize GradientBlinds: Pause animation when off-screen

- Added IntersectionObserver to track component visibility.
- Paused requestAnimationFrame loop when component is not intersecting.
- Resumed loop when component becomes visible.
- Added unit tests to verify start/stop behavior.

src/components/effects/GradientBlinds.tsx

@@ -333,11 +333,28 @@ void main() {
         }
       }
     };
+
+    const observer = new IntersectionObserver(([entry]) => {
+      if (entry.isIntersecting) {
+        if (!rafRef.current) {
+          lastTimeRef.current = 0;
+          rafRef.current = requestAnimationFrame(loop);
+        }
+      } else {
+        if (rafRef.current) {
+          cancelAnimationFrame(rafRef.current);
+          rafRef.current = null;
+        }
+      }
+    });
+    observer.observe(container);
+
     rafRef.current = requestAnimationFrame(loop);
 
     return () => {
       if (rafRef.current) cancelAnimationFrame(rafRef.current);
       canvas.removeEventListener('pointermove', onPointerMove);
+      observer.disconnect();
       ro.disconnect();
       if (canvas.parentElement === container) {
         container.removeChild(canvas);