Block auto-account creation when signing in via GitHub from login mode.
Signup via GitHub now shows a name confirmation dialog before redirecting
to dashboard, letting users verify/edit their display name pulled from
GitHub.
- Add intent query param to OAuth redirect, persisted in HMAC-signed state cookie
- Block registration in callback when intent=login, return no_account error
- Set wrenn_oauth_new_signup cookie on new account creation
- Frontend callback shows name confirmation dialog for new signups
- Add no_account error message to login page
pptx704
6a6b489471