refactor(motion): extraer useEnVista, compartido por las ilustraciones

lib/__tests__/motion.test.tsx

@@ -0,0 +1,24 @@
+import { render } from '@testing-library/react';
+import { describe, it, expect } from 'vitest';
+import { useEnVista } from '@/lib/motion';
+
+function Sonda() {
+  const { ref, enVista, reduced } = useEnVista();
+  return <svg ref={ref} data-en-vista={String(enVista)} data-reducido={String(reduced)} />;
+}
+
+describe('useEnVista', () => {
+  it('hands back a ref to attach, plus the two flags a drawing needs', () => {
+    const { container } = render(<Sonda />);
+    const svg = container.querySelector('svg');
+    expect(svg).toHaveAttribute('data-en-vista');
+    expect(svg).toHaveAttribute('data-reducido');
+  });
+
+  it('starts out not-yet-in-view so drawings do not skip their entrance', () => {
+    const { container } = render(<Sonda />);
+    // jsdom's IntersectionObserver stub never fires, so this also pins the
+    // safe default: nothing claims to be visible until the observer says so.
+    expect(container.querySelector('svg')).toHaveAttribute('data-en-vista', 'false');
+  });
+});