Add missing function exports to library files

QA scan found 4 library files with functions that weren't exported,
making them unavailable in subshells and nested calls.

Added export statements for:
- lib/attack-signatures.sh: 3 functions
- lib/http-attack-analyzer.sh: 5 functions
- lib/email-functions.sh: 18 functions
- lib/rate-anomaly-detector.sh: 9 functions

Total: 35 functions now properly exported

This ensures functions are available when libraries are sourced by
scripts that spawn subshells or use process substitution.

lib/email-functions.sh

@@ -291,3 +291,23 @@ if ! type detect_control_panel &>/dev/null; then
         fi
     }
 fi
+
+# Export functions for use in subshells
+export -f detect_mta
+export -f get_mail_log_path
+export -f get_mailbox_base_path
+export -f validate_email
+export -f get_email_domain
+export -f get_email_local
+export -f format_size
+export -f check_mta_running
+export -f get_mta_version
+export -f get_queue_count
+export -f check_dns_record
+export -f get_primary_ip
+export -f is_valid_ip
+export -f get_reverse_dns
+export -f send_test_email
+export -f parse_exim_email
+export -f get_log_date_range
+export -f count_by_sender