Use Account Names on AWS IAM Identity Center Session Alongside ID

## Problem

The AWS IAM Identity Center integration doesn't show account names for the sessions to select, only the account ID and permissions set.

## Expected behavior

Both the session sellect screen and the current session tooltip on the bottom of VSCode should show the account name and ID, just as the Identity Center start page does, to ensure users know exactly which named account they are logged into.

Start by tracing the AWS IAM Identity Center session-selection entry point and the current-session tooltip in the VS Code extension. Check how the integration currently exposes the account ID and permissions set, then identify the account-name data available from the Identity Center flow. Done means both the session selection screen and bottom tooltip show the account name alongside the account ID.

Written by the indexing model from the issue text.