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/http-attack-analyzer.sh

@@ -293,3 +293,10 @@ format_threat_display() {
     echo "  URI: ${URI:0:100}"
     [ -n "$SIGNATURES" ] && echo "  Signatures: $SIGNATURES"
 }
+
+# Export functions for use in subshells
+export -f analyze_http_log_line
+export -f analyze_http_log_batch
+export -f monitor_http_log_realtime
+export -f parse_http_analysis_result
+export -f format_threat_display