perf: pause GradientBlinds animation when off-screen

Removes the unconditional start of the animation loop on mount. The loop is now exclusively managed by the existing IntersectionObserver, ensuring it only runs when the component is visible.

Updates tests to reflect this behavior by simulating intersection events to trigger the animation.

src/components/effects/GradientBlinds.test.tsx

@@ -66,8 +66,17 @@ describe('GradientBlinds', () => {
     vi.clearAllMocks();
   });
 
-  it('starts animation loop on mount', () => {
+  it('does not start animation loop on mount until visible', () => {
     const { unmount } = render(<GradientBlinds />);
+    expect(rafSpy).not.toHaveBeenCalled();
+
+    // Simulate on-screen
+    act(() => {
+      if (ioCallback) {
+        ioCallback([{ isIntersecting: true } as IntersectionObserverEntry]);
+      }
+    });
+
     expect(rafSpy).toHaveBeenCalled();
     unmount();
     expect(cancelRafSpy).toHaveBeenCalled();
@@ -76,7 +85,15 @@ describe('GradientBlinds', () => {
   it('pauses animation loop when off-screen and resumes when on-screen', () => {
     const { unmount } = render(<GradientBlinds />);
 
-    // Initial start
+    // Should not start initially
+    expect(rafSpy).not.toHaveBeenCalled();
+
+    // Simulate on-screen (start)
+    act(() => {
+      if (ioCallback) {
+        ioCallback([{ isIntersecting: true } as IntersectionObserverEntry]);
+      }
+    });
     expect(rafSpy).toHaveBeenCalledTimes(1);
 
     // Reset spies to check for subsequent calls