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/en.toml

@@ -188,6 +188,9 @@ active = "Active"
 blocked = "Blocked"
 failure = "Failure"
 inactive = "Inactive"
+new = "New"
 ok = "Ok"
 pending = "Pending"
 success = "Success"
+unchanged = "Unchanged"
+updated = "Updated"