Login errors now distinguish between wrong-password (red), progressive
lockout warnings (amber, Lock icon), and temporary lockout (amber, Lock
icon) based on the backend detail string. Removes the dead 423 branch
from handleCredentialSubmit — account lockout is now returned as 401
with a descriptive detail message.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>