Twilio credential validator throws on null input

[rissrice2105-agent]

Summary

validateTwilioCredentials() advertises a structured { valid, errors } result, but it throws when called with null, undefined, or another non-object value because it immediately reads credentials.accountSid.

Reproduction

validateTwilioCredentials(null);

Current behavior

Throws TypeError: Cannot read properties of null.

Expected behavior

Return a structured validation failure, consistent with other invalid credential cases.

Impact

Settings/debug flows that pass missing or malformed credential config can crash instead of showing a recoverable validation error.