feat(user): support fixed UUID registration and enhance bulk import results

- Added support for fixed UUIDs during bulk registration (Search-first + ExternalID mapping)
- Implemented idempotency and visibility restoration for soft-deleted users
- Enhanced bulk upload UI to show 'New/Updated/Unchanged' status and modified fields
- Added logic to reclaim identifiers (login_id) from colliding records
- Added frontend E2E and backend unit tests for UUID integrity and conflict handling
- Fixed i18n, formatting, and mock tests to satisfy code-check
- Applied 'go fix' for 'omitzero' tags and general Go standards

common/locales/ko.toml

@@ -188,6 +188,9 @@ active = "활성"
 blocked = "차단됨"
 failure = "실패"
 inactive = "비활성"
+new = "신규"
 ok = "정상"
 pending = "준비 중"
 success = "성공"
+unchanged = "동일"
+updated = "수정"