Adding 2fa fails with redirect loop

### Environment

SaaS (https://sentry.io/)

### Steps to Reproduce

1. Add 2fa as an passkey or totp device
2. Enroll device, UI says enrolled
3. Press confirm
4. UI redirects back to device enrollment UI without actually adding the device

### Expected Result

2FA device in enrolled.

### Actual Result

2FA device is not enrolled without error in the UI.

### Product Area

Settings - Auth

### Link

https://sentry.io/settings/account/security/mfa/u2f/enroll/

### DSN

_No response_

### Version

_No response_

Start by reproducing the failure at the linked MFA enrollment URL using the listed passkey or TOTP steps. Trace the confirmation flow for the redirect back to device enrollment and compare it with the expected enrolled-device state. Done means confirming the device succeeds without a redirect loop and the UI reflects enrollment.

Written by the indexing model from the issue text.