* allow smtp server that does not have authentication
* fix: align checkEmailConfig with optional SMTP credentials and add tests
Remove EMAIL_USERNAME/EMAIL_PASSWORD requirements from the hasSMTPConfig
predicate in checkEmailConfig() so the rest of the codebase (login,
startup checks, invite-user) correctly recognizes unauthenticated SMTP
as a valid email configuration.
Add a warning when only one of the two credential env vars is set,
in both sendEmail.js and checkEmailConfig(), to catch partial
misconfigurations early.
Add test coverage for both the transporter auth assembly in sendEmail.js
and the checkEmailConfig predicate in packages/api.
Document in .env.example that credentials are optional for
unauthenticated SMTP relays.
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Co-authored-by: Danny Avila <danny@librechat.ai>
