fix: 대체 아이템 삭제와 미사용 정리 기준 보정

frontend/src/views/AdminView.vue

@@ -657,6 +657,14 @@ const visibleLinkedTemplates = computed(() =>
 const linkedCustomItemTemplateIds = computed(() => new Set(visibleLinkedTemplates.value.map((template) => template.id).filter(Boolean)))
 const canReplaceModalTarget = computed(() => modalTargetCustomItem.value?.sourceType === 'user')
 const replacementCandidateCount = computed(() => customItemReplacementItems.value.length)
+const hasDeletableUnusedCustomItems = computed(() =>
+  customItems.value.some(
+    (item) =>
+      item?.sourceType === 'user' &&
+      (!!item.replacedAt ||
+        (Number(item.usageCount || 0) === 0 && !(Array.isArray(item.linkedTemplates) && item.linkedTemplates.length > 0)))
+  )
+)
 
 const imageStatsPeriodLabel = computed(() => (imageStatsMonth.value ? `${imageStatsMonth.value} 기준` : '전체 기간'))
 const imageStatsYearOptions = computed(() => {
@@ -2454,7 +2462,7 @@ function openUserProfile(user) {
         </div>
         <div class="adminSidebar__actions">
           <button class="btn btn--ghost" @click="refreshCustomItems">새로고침</button>
-          <button class="btn btn--danger" :disabled="customItemFilter !== 'unused-user' || !customItems.length" @click="removeUnusedCustomItems">미사용 아이템 일괄 삭제</button>
+          <button class="btn btn--danger" :disabled="customItemFilter !== 'unused-user' || !hasDeletableUnusedCustomItems" @click="removeUnusedCustomItems">미사용 아이템 일괄 삭제</button>
         </div>
         <div class="adminSidebar__stats">
           <div class="sidebarStat">