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/composables/useDragReorder.ts

@@ -0,0 +1,109 @@
+import { ref } from 'vue'
+
+interface DragReorderHandlers {
+  draggingIndex: Ref<number | null>
+  dropTargetIndex: Ref<number | null>
+  onDragStart: (index: number, event: DragEvent) => void
+  onDragEnter: (index: number) => void
+  onDragOver: (event: DragEvent) => void
+  onDrop: (index: number) => void
+  onDragEnd: () => void
+  reorderClass: (index: number) => string
+  reset: () => void
+}
+
+interface DragReorderOptions {
+  draggingClass?: string
+  dropTargetClass?: string
+  onReorder?: () => void
+}
+
+function moveItemInPlace<T>(list: T[], from: number, to: number): void {
+  if (from === to) return
+  if (from < 0 || to < 0 || from >= list.length || to >= list.length) return
+  const updated = list.slice()
+  const [item] = updated.splice(from, 1)
+  if (item === undefined) return
+  updated.splice(to, 0, item)
+  list.splice(0, list.length, ...updated)
+}
+
+export function useDragReorder(
+  getList: () => unknown[] | undefined,
+  options: DragReorderOptions = {},
+): DragReorderHandlers {
+  const {
+    draggingClass = 'border-dashed border-primary',
+    dropTargetClass = 'border-primary border-dashed bg-primary/5',
+    onReorder,
+  } = options
+
+  const draggingIndex = ref<number | null>(null)
+  const dropTargetIndex = ref<number | null>(null)
+
+  const reset = () => {
+    draggingIndex.value = null
+    dropTargetIndex.value = null
+  }
+
+  const onDragStart = (index: number, event: DragEvent) => {
+    draggingIndex.value = index
+    dropTargetIndex.value = index
+    if (event.dataTransfer) {
+      event.dataTransfer.effectAllowed = 'move'
+    }
+  }
+
+  const onDragEnter = (index: number) => {
+    if (draggingIndex.value === null) return
+    dropTargetIndex.value = index
+  }
+
+  const onDragOver = (event: DragEvent) => {
+    event.preventDefault()
+  }
+
+  const onDrop = (index: number) => {
+    const list = getList()
+    if (!Array.isArray(list)) {
+      reset()
+      return
+    }
+    const from = draggingIndex.value
+    if (from === null) {
+      reset()
+      return
+    }
+    moveItemInPlace(list, from, index)
+    onReorder?.()
+    reset()
+  }
+
+  const onDragEnd = () => {
+    reset()
+  }
+
+  const reorderClass = (index: number): string => {
+    if (draggingIndex.value === index) return draggingClass
+    if (
+      draggingIndex.value !== null
+      && dropTargetIndex.value === index
+      && draggingIndex.value !== index
+    ) {
+      return dropTargetClass
+    }
+    return ''
+  }
+
+  return {
+    draggingIndex,
+    dropTargetIndex,
+    onDragStart,
+    onDragEnter,
+    onDragOver,
+    onDrop,
+    onDragEnd,
+    reorderClass,
+    reset,
+  }
+}