fix(knowledge): remove backup load check causing duplicate items on scroll

The IntersectionObserver fires as soon as it's created (sentinel immediately
intersecting after page 1 renders), while the removed backup check also fires
in the same tick — two concurrent fetchItems(page 2) calls produced duplicate
cards. With sentinel now properly inside the scrolling root, the observer
alone handles progressive loading.

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

frontend/src/views/KnowledgeView.vue

@@ -82,19 +82,6 @@ async function fetchItems(reset = false) {
   } finally {
     loading.value = false;
   }
-
-  // If the sentinel is still visible in the card-grid after appending, keep loading
-  if (!reset && items.value.length < total.value) {
-    await nextTick();
-    if (sentinelEl.value && cardGridEl.value) {
-      const containerBottom = cardGridEl.value.getBoundingClientRect().bottom;
-      const sentinelTop = sentinelEl.value.getBoundingClientRect().top;
-      if (sentinelTop < containerBottom + 200) {
-        page.value++;
-        await fetchItems();
-      }
-    }
-  }
 }
 
 async function fetchTags() {