Add automatic testimonial rotation with timer functionality in Testimonials component

src/components/Testimonials.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import { onMount, onDestroy } from 'svelte';
   const testimonials = [
     {
       name: 'Sarah Johnson',
@@ -21,14 +22,31 @@
   ];
 
   let currentIndex = 0;
+  let timer: ReturnType<typeof setTimeout>;
+  const ROTATE_INTERVAL = 20000; // 20 seconds
 
-  function next() {
+  function next(reset = true) {
     currentIndex = (currentIndex + 1) % testimonials.length;
+    if (reset) resetTimer();
   }
 
   function prev() {
     currentIndex = (currentIndex - 1 + testimonials.length) % testimonials.length;
+    resetTimer();
   }
+
+  function resetTimer() {
+    clearTimeout(timer);
+    timer = setTimeout(() => next(false), ROTATE_INTERVAL);
+  }
+
+  onMount(() => {
+    timer = setTimeout(() => next(false), ROTATE_INTERVAL);
+  });
+
+  onDestroy(() => {
+    clearTimeout(timer);
+  });
 </script>
 
 <section class="py-20 bg-surface">