feat(ui): add infinite scroll pagination to chat completions/responses logs table (#2466)

## Summary:

This commit adds infinite scroll pagination to the chat completions and
responses tables.


## Test Plan:
  1. Run unit tests: npm run test
  2. Manual testing: Navigate to chat
  completions/responses pages
  3. Verify infinite scroll triggers when approaching
  bottom
  4. Added playwright tests: npm run test:e2e

llama_stack/ui/hooks/useInfiniteScroll.ts

@@ -0,0 +1,55 @@
+"use client";
+
+import { useRef, useEffect } from "react";
+
+interface UseInfiniteScrollOptions {
+  /** Whether the feature is enabled (e.g., hasMore data) */
+  enabled?: boolean;
+  /** Threshold for intersection (0-1, how much of sentinel must be visible) */
+  threshold?: number;
+  /** Margin around root to trigger earlier (e.g., "100px" to load 100px before visible) */
+  rootMargin?: string;
+}
+
+/**
+ * Custom hook for infinite scroll using Intersection Observer
+ *
+ * @param onLoadMore - Callback to load more data
+ * @param options - Configuration options
+ * @returns ref to attach to sentinel element
+ */
+export function useInfiniteScroll(
+  onLoadMore: (() => void) | undefined,
+  options: UseInfiniteScrollOptions = {},
+) {
+  const { enabled = true, threshold = 0.1, rootMargin = "100px" } = options;
+  const sentinelRef = useRef<HTMLTableRowElement>(null);
+
+  useEffect(() => {
+    if (!onLoadMore || !enabled) return;
+
+    const observer = new IntersectionObserver(
+      (entries) => {
+        const [entry] = entries;
+        if (entry.isIntersecting) {
+          onLoadMore();
+        }
+      },
+      {
+        threshold,
+        rootMargin,
+      },
+    );
+
+    const sentinel = sentinelRef.current;
+    if (sentinel) {
+      observer.observe(sentinel);
+    }
+
+    return () => {
+      observer.disconnect();
+    };
+  }, [onLoadMore, enabled, threshold, rootMargin]);
+
+  return sentinelRef;
+}