Connect MCP: tool calls can return 413 account_limit_reached for external users with far fewer than 100 live accounts

## Summary

Connect MCP tool calls for an external user can fail with a `413 account_limit_reached` response:

```
{
"error": "account_limit_reached",
"message": "External user has more than 100 accounts. Use /v1/connect/{project_id}/accounts for the full paginated list"
}
```

even when that external user has well under 100 connected accounts.

Start by reproducing a Connect MCP tool call for an external user with well under 100 live accounts and inspect the account-count logic behind the 413 response. Trace the handling of the `/v1/connect/{project_id}/accounts` endpoint and verify that the call succeeds without `account_limit_reached` until the documented limit is actually reached.

Written by the indexing model from the issue text.