CVE-2026-45675: Open WebUI: LDAP and OAuth First-User Race Condition Allows Multiple Admin Accounts

The LDAP and OAuth authentication flows use a TOCTOU (Time-of-Check-Time-of-Use) pattern for first-user admin role assignment. The regular signup handler (signup_handler in auths.py, line 663) was explicitly patched to prevent this race with the comment “Insert with default role first to avoid TOCTOU race”, but the LDAP and OAuth code paths were never updated with the same fix.