refactor(frontend) : extract shared components and reduce file sizes

- Extract CustomFieldInputGrid.vue from 6 duplicated template blocks (~70 lines each)
- Extract EntityHistorySection.vue from 3 identical history sections in edit pages
- Extract useDragReorder composable from 4 identical drag-and-drop implementations in StructureNodeEditor (~330 lines → ~30)
- Extract catalogDisplayUtils.ts (resolvePrimaryDocument, resolveSupplierNames, buildSuppliersDisplay)
- Remove redundant computed wrappers (historyEntries, loadingTypes, selectedFiles)
- Remove unused imports (fieldKey, historyActionLabel, formatHistoryDate, *HistoryEntry types)
- Move Intl.DateTimeFormat to module-level in date.ts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/pages/documents.vue

@@ -3,7 +3,7 @@
     <DocumentPreviewModal
       :document="previewDocument"
       :visible="previewVisible"
-      :documents="documentRows"
+      :documents="documents"
       @close="closePreview"
     />
 
@@ -11,7 +11,7 @@
       <div class="card-body space-y-6">
         <DataTable
           :columns="columns"
-          :rows="documentRows"
+          :rows="documents"
           :loading="loading"
           :sort="table.sort.value"
           :pagination="paginationState"
@@ -148,7 +148,6 @@ const attachmentFilter = table.filters.filter as Ref<string>
 const previewDocument = ref<any>(null)
 const previewVisible = ref(false)
 
-const documentRows = computed(() => documents.value)
 const documentsOnPage = computed(() => documents.value.length)
 const paginationState = table.pagination(total, documentsOnPage)