[codex] Fix sign-in submit and federated auth reset

[JamieRuderman]

Summary

• Add explicit Enter-key submission for the Cognito sign-in form so Enter advances the email step and submits the password step.
• Reset sign-in loading state and surface errors when Google/Apple federated sign-in returns or fails without leaving the page.
• Sync returned sign-in errors into the sign-in component and await SAML/federated handlers through typed auth props.

Root Cause

The sign-in view set loading before federated auth but had no catch/finally path if the hosted UI flow failed or returned to the same page, leaving the social buttons and form disabled. The form also relied on implicit browser submit behavior; making Enter submission explicit avoids UI/control edge cases in the multi-step Cognito form.

Validation

• npm run typecheck
• npm run build
• Browser smoke test on http://127.0.0.1:3003/sign-in: Enter on email advances to password, Enter on password submits, Cognito error renders, and the form remains usable.

[aws-amplify-us-west-1]

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