Couldn't signin through pro account inspite of having kiro pro

## Problem

## Steps to reproduce the issue

## Expected behavior

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS:
- Visual Studio Code version:
- AWS Toolkit version:
- Amazon Q version:

Start by reproducing the sign-in problem in the VS Code extension and collect the missing OS, Visual Studio Code, AWS Toolkit, and Amazon Q versions requested in the issue. Check the AWS: About and Amazon Q: About entry points, record the exact error, and consider the issue complete only when Kiro Pro sign-in succeeds or the failure is narrowed to a documented cause.

Written by the indexing model from the issue text.