- 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
- Add `ValidateLoginID` to enforce ID collision and security rules (prevents phone number collision, email format usage, and reserved words).
- Add `POST /api/v1/auth/signup/check-login-id` endpoint for real-time ID availability checks.
- Add `checkLoginIDAvailability` API call to userfront's `AuthProxyService`.
- Implement "Check Duplication" button and error/success messaging for the Login ID field in the signup screen.
- Add "000000" magic code bypass for `VerifySignupCode` in non-production environments to streamline testing.
