9c04b3c198
CodeQL flagged critical vulnerabilities in mail_service.go where untrusted input could be used to inject additional email headers via CRLF sequences. Changes: - Add sanitizeEmailHeader() to strip CR, LF, and control characters - Sanitize all header values (from, to, subject) in buildEmail() - Add validateEmailAddress() using net/mail.ParseAddress - Add comprehensive security tests for header injection prevention This addresses the 3 critical CodeQL alerts: - Line 199: buildEmail header construction - Line 260: sendSSL message usage - Line 307: sendSTARTTLS message usage Security: CWE-93 (Improper Neutralization of CRLF Sequences)