fix: remove hardcoded passwords and enhance security in production setup

Security Enhancements:
- Update .gitignore header timestamp to 2026-03-18 for security fixes
- Add CRITICAL SECURITY markers to sensitive sections in .gitignore
- Add comprehensive password file patterns (*.password, *.pass, .password.*)
- Add private key file patterns (*_private_key.txt, *.private, private_key.*)
- Add guardian contract database patterns (*.guardian.db, guardian_contracts/)
- Add multi-chain wallet data patterns (.

scripts/implement-agent-protocols.sh

@@ -352,7 +352,11 @@ class MessageProtocol:
     
     def _generate_key(self) -> bytes:
         """Generate encryption key"""
-        password = os.environ.get('AITBC_AGENT_PROTOCOL_KEY', b"default-key-change-in-production")
+        # SECURITY FIX: Use environment variable instead of hardcoded default
+        password = os.environ.get('AITBC_AGENT_PROTOCOL_KEY')
+        if not password:
+            raise ValueError("❌ SECURITY: AITBC_AGENT_PROTOCOL_KEY environment variable required")
+        
         salt = os.environ.get('AITBC_AGENT_PROTOCOL_SALT', b"aitbc-salt-agent-protocol")
         if isinstance(password, str):
             password = password.encode()