fix: 대체된 사용자 아이템 보존 및 상태 표시

backend/src/routes/admin.js

@@ -33,6 +33,7 @@ const {
   findUnusedCustomItems,
   findCustomItemsByIds,
   deleteCustomItems,
+  markCustomItemReplaced,
   listUsers,
   findPrimaryAdminUser,
   listAdminTierLists,
@@ -835,10 +836,12 @@ router.post('/custom-items/:itemId/replace', requireAdmin, async (req, res) => {
     toSrc: targetItem.src,
     toLabel: targetItem.label || '',
   })
-
-  const sourceCustomItems = await findCustomItemsByIds([sourceItem.id])
-  await deleteCustomItems([sourceItem.id])
-  await removeCustomItemFiles(sourceCustomItems)
+  await markCustomItemReplaced({
+    itemId: sourceItem.id,
+    replacedByItemId: targetItem.id || '',
+    replacedBySrc: targetItem.src || '',
+    replacedByLabel: targetItem.label || '',
+  })
 
   res.json({
     ok: true,