refactor: 품목기준관리 설정 페이지 훅/컴포넌트 분리

- Phase 1: 신규 훅 4개 생성
  - useInitialDataLoading.ts (초기 데이터 로딩)
  - useImportManagement.ts (섹션/필드 Import)
  - useReorderManagement.ts (드래그앤드롭 순서 변경)
  - useDeleteManagement.ts (삭제/언링크 핸들러)
- Phase 2: UI 컴포넌트 2개 생성
  - AttributeTabContent.tsx (속성 탭 콘텐츠)
  - ItemMasterDialogs.tsx (다이얼로그 통합)
- 메인 컴포넌트 1,799줄 → ~1,478줄 (약 320줄 감소)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/items/ItemMasterDataManagement/hooks/useInitialDataLoading.ts

@@ -0,0 +1,150 @@
+'use client';
+
+import { useState, useEffect, useCallback } from 'react';
+import { useItemMaster } from '@/contexts/ItemMasterContext';
+import { itemMasterApi } from '@/lib/api/item-master';
+import { getErrorMessage, ApiError } from '@/lib/api/error-handler';
+import {
+  transformPagesResponse,
+  transformSectionsResponse,
+  transformSectionTemplatesResponse,
+  transformFieldsResponse,
+  transformCustomTabsResponse,
+  transformUnitOptionsResponse,
+  transformSectionTemplateFromSection,
+} from '@/lib/api/transformers';
+import { toast } from 'sonner';
+import type { CustomTab } from './useTabManagement';
+import type { UnitOption } from './useAttributeManagement';
+
+export interface UseInitialDataLoadingReturn {
+  isInitialLoading: boolean;
+  error: string | null;
+  reload: () => Promise<void>;
+}
+
+interface UseInitialDataLoadingProps {
+  setCustomTabs: React.Dispatch<React.SetStateAction<CustomTab[]>>;
+  setUnitOptions: React.Dispatch<React.SetStateAction<UnitOption[]>>;
+}
+
+export function useInitialDataLoading({
+  setCustomTabs,
+  setUnitOptions,
+}: UseInitialDataLoadingProps): UseInitialDataLoadingReturn {
+  const {
+    loadItemPages,
+    loadSectionTemplates,
+    loadItemMasterFields,
+    loadIndependentSections,
+    loadIndependentFields,
+  } = useItemMaster();
+
+  const [isInitialLoading, setIsInitialLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  const loadInitialData = useCallback(async () => {
+    try {
+      setIsInitialLoading(true);
+      setError(null);
+
+      const data = await itemMasterApi.init();
+
+      // 1. 페이지 데이터 로드 (섹션이 이미 포함되어 있음)
+      const transformedPages = transformPagesResponse(data.pages);
+      loadItemPages(transformedPages);
+
+      // 2. 독립 섹션 로드 (모든 재사용 가능 섹션)
+      if (data.sections && data.sections.length > 0) {
+        const transformedSections = transformSectionsResponse(data.sections);
+        loadIndependentSections(transformedSections);
+        console.log('✅ 독립 섹션 로드:', transformedSections.length);
+      }
+
+      // 3. 섹션 템플릿 로드
+      if (data.sectionTemplates && data.sectionTemplates.length > 0) {
+        const transformedTemplates = transformSectionTemplatesResponse(data.sectionTemplates);
+        loadSectionTemplates(transformedTemplates);
+      } else if (data.sections && data.sections.length > 0) {
+        const templates = data.sections
+          .filter((s: { is_template?: boolean }) => s.is_template)
+          .map(transformSectionTemplateFromSection);
+        if (templates.length > 0) {
+          loadSectionTemplates(templates);
+        }
+      }
+
+      // 4. 필드 로드
+      if (data.fields && data.fields.length > 0) {
+        const transformedFields = transformFieldsResponse(data.fields);
+
+        const independentOnlyFields = transformedFields.filter(
+          f => f.section_id === null || f.section_id === undefined
+        );
+
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        loadItemMasterFields(transformedFields as any);
+        loadIndependentFields(independentOnlyFields);
+
+        console.log('✅ 필드 로드:', {
+          total: transformedFields.length,
+          independent: independentOnlyFields.length,
+        });
+      }
+
+      // 5. 커스텀 탭 로드
+      if (data.customTabs && data.customTabs.length > 0) {
+        const transformedTabs = transformCustomTabsResponse(data.customTabs);
+        setCustomTabs(transformedTabs);
+      }
+
+      // 6. 단위 옵션 로드
+      if (data.unitOptions && data.unitOptions.length > 0) {
+        const transformedUnits = transformUnitOptionsResponse(data.unitOptions);
+        setUnitOptions(transformedUnits);
+      }
+
+      console.log('✅ Initial data loaded:', {
+        pages: data.pages?.length || 0,
+        sections: data.sections?.length || 0,
+        fields: data.fields?.length || 0,
+        customTabs: data.customTabs?.length || 0,
+        unitOptions: data.unitOptions?.length || 0,
+      });
+
+    } catch (err) {
+      if (err instanceof ApiError && err.errors) {
+        const errorMessages = Object.entries(err.errors)
+          .map(([field, messages]) => `${field}: ${messages.join(', ')}`)
+          .join('\n');
+        toast.error(errorMessages);
+        setError('입력값을 확인해주세요.');
+      } else {
+        const errorMessage = getErrorMessage(err);
+        setError(errorMessage);
+        toast.error(errorMessage);
+      }
+      console.error('❌ Failed to load initial data:', err);
+    } finally {
+      setIsInitialLoading(false);
+    }
+  }, [
+    loadItemPages,
+    loadSectionTemplates,
+    loadItemMasterFields,
+    loadIndependentSections,
+    loadIndependentFields,
+    setCustomTabs,
+    setUnitOptions,
+  ]);
+
+  useEffect(() => {
+    loadInitialData();
+  }, [loadInitialData]);
+
+  return {
+    isInitialLoading,
+    error,
+    reload: loadInitialData,
+  };
+}