[Bug]: Amazon login fails with "We're unable to verify your mobile number" or redirects to /ap/maplanding

### Describe the bug

### System information

- Home Assistant Core: 2026.7.2
- Home Assistant Supervisor: 2026.06.2
- Home Assistant OS: 18.1
- Alexa Media Player: 5.15.6
- Amazon region: amazon.de
- 2FA: Enabled with authenticator app
- Verified mobile phone number: Yes

### Problem

I am unable to complete the initial setup of Alexa Media Player.

In Edge, the Amazon login immediately shows:

"We're unable to verify your mobile number. Try signing in again."

In Firefox, the login process goes further, but eventually redirects to:

www.amazon.com/ap/maplanding

Amazon then displays an error saying that the requested page is not functional.

### Configuration

- Amazon region: amazon.de
- Local Home Assistant URL: http://192.168.x.x:8123
- External URL: Home Assistant Cloud / Nabu Casa URL
- 52-character authenticator app key configured

### Troubleshooting already performed

- Updated Alexa Media Player to 5.15.6
- Restarted Home Assistant
- Tested with Firefox and Edge
- Confirmed that the Amazon mobile number is verified
- Confirmed that Amazon 2FA with an authenticator app is enabled
- Confirmed that the 52-character authenticator key is configured
- Tested with the correct local Home Assistant URL
- Debug logging confirmed that Alexa Media Player is installed and the authentication flow starts

The integration is never added to the configured integrations because the Amazon authentication flow does not complete.

Is this a known issue with the current Amazon authentication flow, and is there a workaround?

### To Reproduce

### System information

- Home Assistant Core: 2026.7.2
- Home Assistant Supervisor: 2026.06.2
- Home Assistant OS: 18.1
- Alexa Media Player: 5.15.6
- Amazon region: amazon.de
- 2FA: Enabled with authenticator app
- Verified mobile phone number: Yes

### Expected behavior

### System information

- Home Assistant Core: 2026.7.2
- Home Assistant Supervisor: 2026.06.2
- Home Assistant OS: 18.1
- Alexa Media Player: 5.15.6
- Amazon region: amazon.de
- 2FA: Enabled with authenticator app
- Verified mobile phone number: Yes

### Screenshots

_No response_

### Home Assistant Version

2026.7.2

### Alexa Media Player Version

5.15.6

### Alexa Media Player API library Version

1.29.25

### Have you entered a 52-character key for Amazon 2SV via Authenticator App login?

Yes

### Is the HA core integration Alexa Devices installed?

No

### Amazon Domain

amazon.de (Germany)

### Amazon Domain (if Other)

_No response_

### Debug Logs (alexa_media & alexapy)

I have attached a Home Assistant debug log captured immediately after reproducing the Alexa Media Player login issue.

The login fails during the Amazon authentication flow. In Edge, Amazon reports that the mobile number cannot be verified. In Firefox, authentication proceeds further but ends at amazon.com/ap/maplanding.

Sensitive authentication information has been redacted from the attached log.

### Additional context

_No response_