chore(security): add gitignore entries for audit artifacts

Prevent AUDIT_REPORT.md and .plamen*/ scratchpads from being
accidentally committed to this public repo.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: twzrd-sol

.gitignore

@@ -5,3 +5,8 @@ dump.so
 *.so
 .env
 test-ledger/
+
+# Audit artifacts — never commit to public repo
+.plamen*/
+AUDIT_REPORT.md
+AUDIT_REPORT_*.md