[Screenshot] Fix broken portallogin.png on SSO login page

**Page:** `macstadium/account-management-and-saml/first-time-sso-login-to-macstadium-portal.mdx`

The image `portallogin.png` is broken on this page. Someone needs to log in to the MacStadium portal and retake a fresh screenshot of the SSO login flow.

**Action needed:** Retake screenshot of the SSO login page and replace `portallogin.png`.