fix: 대체 아이템 삭제와 미사용 정리 기준 보정

backend/src/routes/admin.js

@@ -54,6 +54,7 @@ const {
   listRecentImageOptimizationJobs,
   clearImageOptimizationJobs,
   cleanupMissingUploadReferences,
+  listReferencedUploadSources,
   replaceUploadSourceReferences,
   updateCustomItemDisplayReferences,
   clearCustomItemReplacement,
@@ -546,6 +547,12 @@ async function removeCustomItemFiles(items) {
   )
 }
 
+async function removeUnreferencedCustomItemFiles(items) {
+  const referencedSrcs = new Set(await listReferencedUploadSources())
+  const removableItems = (items || []).filter((item) => item?.src && !referencedSrcs.has(item.src))
+  await removeCustomItemFiles(removableItems)
+}
+
 async function promoteLibraryItemToTemplateItem({ item, templateId }) {
   return createTopicItem({
     id: nanoid(),
@@ -776,13 +783,14 @@ router.delete('/custom-items/:itemId', requireAdmin, async (req, res) => {
     return res.json({ ok: true, sourceType: 'template' })
   }
 
+  const canDeleteReplacedUserItem = target.sourceType === 'user' && !!target.replacedAt
   if (!target.canDelete) return res.status(409).json({ error: 'item_locked' })
-  if (target.linkedTemplates.length > 0) return res.status(409).json({ error: 'item_linked' })
-  if (target.usageCount > 0) return res.status(409).json({ error: 'item_in_use' })
+  if (!canDeleteReplacedUserItem && target.linkedTemplates.length > 0) return res.status(409).json({ error: 'item_linked' })
+  if (!canDeleteReplacedUserItem && target.usageCount > 0) return res.status(409).json({ error: 'item_in_use' })
 
   const items = await findCustomItemsByIds([target.id])
   await deleteCustomItems([target.id])
-  await removeCustomItemFiles(items)
+  await removeUnreferencedCustomItemFiles(items)
   res.json({ ok: true, sourceType: 'user' })
 })
 
@@ -1135,7 +1143,7 @@ router.delete('/custom-items', requireAdmin, async (req, res) => {
   const items = await findUnusedCustomItems({ queryText: parsed.data.q })
   const ids = items.map((item) => item.id)
   await deleteCustomItems(ids)
-  await removeCustomItemFiles(items)
+  await removeUnreferencedCustomItemFiles(items)
   res.json({ ok: true, deletedCount: ids.length })
 })