feat: add videoRows utility for big-card list layout

utils/videoRows.ts

@@ -0,0 +1,38 @@
+import type { VideoItem } from '../services/types';
+
+export interface NormalRow {
+  type: 'pair';
+  left: VideoItem;
+  right: VideoItem | null;
+}
+
+export interface BigRow {
+  type: 'big';
+  item: VideoItem;
+}
+
+export type ListRow = NormalRow | BigRow;
+
+/**
+ * Transform a flat VideoItem array into display rows.
+ * The last item always becomes a full-width BigRow.
+ * All preceding items are grouped into NormalRow pairs.
+ */
+export function toListRows(videos: VideoItem[]): ListRow[] {
+  if (videos.length === 0) return [];
+  if (videos.length === 1) return [{ type: 'big', item: videos[0] }];
+
+  const rows: ListRow[] = [];
+  const body = videos.slice(0, videos.length - 1);
+
+  for (let i = 0; i < body.length; i += 2) {
+    rows.push({
+      type: 'pair',
+      left: body[i],
+      right: body[i + 1] ?? null,
+    });
+  }
+
+  rows.push({ type: 'big', item: videos[videos.length - 1] });
+  return rows;
+}