feat: API 통합을 위한 기초 인프라 구축

- 네트워크 레이어 구현 (Dio 기반 ApiClient)
- 환경별 설정 관리 시스템 구축
- 의존성 주입 설정 (GetIt)
- API 엔드포인트 상수 정의
- 인터셉터 구현 (Auth, Error, Logging)
- 프로젝트 아키텍처 개선 (core, data, di 디렉토리 구조)
- API 통합 계획서 및 요구사항 문서 작성
- 필요 패키지 추가 (dio, flutter_secure_storage, get_it 등)

lib/core/constants/api_endpoints.dart

@@ -0,0 +1,77 @@
+/// API 엔드포인트 상수 정의
+class ApiEndpoints {
+  // 인증
+  static const String login = '/auth/login';
+  static const String logout = '/auth/logout';
+  static const String refresh = '/auth/refresh';
+  static const String me = '/me';
+  
+  // 장비 관리
+  static const String equipment = '/equipment';
+  static const String equipmentSearch = '/equipment/search';
+  static const String equipmentIn = '/equipment/in';
+  static const String equipmentOut = '/equipment/out';
+  static const String equipmentBatchOut = '/equipment/batch-out';
+  static const String equipmentManufacturers = '/equipment/manufacturers';
+  static const String equipmentNames = '/equipment/names';
+  static const String equipmentHistory = '/equipment/history';
+  static const String equipmentRentals = '/equipment/rentals';
+  static const String equipmentRepairs = '/equipment/repairs';
+  static const String equipmentDisposals = '/equipment/disposals';
+  
+  // 회사 관리
+  static const String companies = '/companies';
+  static const String companiesSearch = '/companies/search';
+  static const String companiesNames = '/companies/names';
+  static const String companiesCheckDuplicate = '/companies/check-duplicate';
+  static const String companiesWithBranches = '/companies/with-branches';
+  static const String companiesBranches = '/companies/{id}/branches';
+  
+  // 사용자 관리
+  static const String users = '/users';
+  static const String usersSearch = '/users/search';
+  static const String usersChangePassword = '/users/{id}/change-password';
+  static const String usersStatus = '/users/{id}/status';
+  
+  // 라이선스 관리
+  static const String licenses = '/licenses';
+  static const String licensesExpiring = '/licenses/expiring';
+  static const String licensesAssign = '/licenses/{id}/assign';
+  static const String licensesUnassign = '/licenses/{id}/unassign';
+  
+  // 창고 위치 관리
+  static const String warehouseLocations = '/warehouse-locations';
+  static const String warehouseLocationsSearch = '/warehouse-locations/search';
+  static const String warehouseEquipment = '/warehouse-locations/{id}/equipment';
+  static const String warehouseCapacity = '/warehouse-locations/{id}/capacity';
+  
+  // 파일 관리
+  static const String filesUpload = '/files/upload';
+  static const String filesDownload = '/files/{id}';
+  
+  // 보고서
+  static const String reports = '/reports';
+  static const String reportsPdf = '/reports/{type}/pdf';
+  static const String reportsExcel = '/reports/{type}/excel';
+  
+  // 대시보드 및 통계
+  static const String overviewStats = '/overview/stats';
+  static const String overviewRecentActivities = '/overview/recent-activities';
+  static const String overviewEquipmentStatus = '/overview/equipment-status';
+  static const String overviewLicenseExpiry = '/overview/license-expiry';
+  
+  // 대량 처리
+  static const String bulkUpload = '/bulk/upload';
+  static const String bulkUpdate = '/bulk/update';
+  
+  // 감사 로그
+  static const String auditLogs = '/audit-logs';
+  
+  // 백업
+  static const String backupCreate = '/backup/create';
+  static const String backupRestore = '/backup/restore';
+  
+  // 검색 및 조회
+  static const String lookups = '/lookups';
+  static const String categories = '/lookups/categories';
+}