fix(knowledge): debounce scroll handler with rAF to prevent duplicate page loads

Coalesces rapid scroll events into one check per animation frame so
that page++ can only fire once per frame, eliminating the window where
multiple events slip through before loading=true is observed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/KnowledgeView.vue

@@ -245,15 +245,21 @@ function formatDate(iso: string): string {
 // ─── Infinite scroll ──────────────────────────────────────────────────────────
 
 const cardGridEl = ref<HTMLElement | null>(null);
+let scrollRafId: number | null = null;
 
 function onGridScroll() {
-  const el = cardGridEl.value;
-  if (!el || loading.value || items.value.length >= total.value) return;
-  const nearBottom = el.scrollHeight - el.scrollTop - el.clientHeight < 300;
-  if (nearBottom) {
-    page.value++;
-    fetchItems();
-  }
+  // Debounce via rAF — coalesces rapid scroll events into one check per frame
+  if (scrollRafId !== null) return;
+  scrollRafId = requestAnimationFrame(() => {
+    scrollRafId = null;
+    const el = cardGridEl.value;
+    if (!el || loading.value || items.value.length >= total.value) return;
+    const nearBottom = el.scrollHeight - el.scrollTop - el.clientHeight < 300;
+    if (nearBottom) {
+      page.value++;
+      fetchItems();
+    }
+  });
 }
 
 // ─── Lifecycle ────────────────────────────────────────────────────────────────
@@ -266,6 +272,7 @@ onMounted(() => {
 
 onUnmounted(() => {
   if (searchDebounce) clearTimeout(searchDebounce);
+  if (scrollRafId !== null) cancelAnimationFrame(scrollRafId);
 });
 </script>