SEO tweaks, design tweaks

vitest.setup.ts

@@ -14,7 +14,19 @@ vi.mock('canvas-confetti', () => ({
 }));
 
 class MockIntersectionObserver {
-  observe() {}
+  private callback: IntersectionObserverCallback;
+
+  constructor(callback: IntersectionObserverCallback) {
+    this.callback = callback;
+  }
+
+  observe(target: Element) {
+    this.callback(
+      [{ isIntersecting: true, target } as IntersectionObserverEntry],
+      this as unknown as IntersectionObserver
+    );
+  }
+
   unobserve() {}
   disconnect() {}
 }