Authentication succeeds but Alexa Media Player fails to complete setup on Home Assistant 2026.7.4

### Checklist
- [x] I have searched existing issues.
- [x] I am using the latest Alexa Media Player version.
- [x] I have restarted Home Assistant.
- [x] I have removed and reinstalled the integration.

### System
- Home Assistant Core: 2026.7.4
- Home Assistant OS: 18.1
- HACS: Latest
- Alexa Media Player: 5.15.7

### Problem
The integration does not complete authentication.
I enter:
- Amazon region: amazon.com (also tested amazon.sa)
- Email
- Password
Amazon sends the OTP code successfully.
After entering the OTP, authentication does not complete and the integration returns to the login page or fails to finish setup.

### What I already tested
- Removed and reinstalled Alexa Media Player.
- Restarted Home Assistant.
- Home Assistant Cloud is connected and Alexa is linked.
- Amazon account works normally.
- Alexa Web works normally.
- GitHub account is working.
- Tried amazon.com and amazon.sa.
- No errors appear in Home Assistant Core logs or Repairs.

### Expected behavior
The integration should complete authentication and create the Alexa devices.

### Actual behavior
Authentication never completes even though Amazon accepts the login and OTP successfully.

### Have you entered a 52-character key for Amazon 2SV via Authenticator App login?
No

### Is the HA core integration Alexa Devices installed?
No

### Amazon Domain
amazon.com (US)

#### **_Any ideas or known compatibility issues with Home Assistant Core 2026.7.4?_**