C-01: verifyTotp now sends backup_code field when in backup mode
C-02: Backup code input filter allows alphanumeric chars (not digits only)
W-01: Audit log ACTION_TYPES aligned with actual backend action strings
W-02: Added extra="forbid" to SetupRequest and LoginRequest schemas
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>