Make extractPassthroughProps more resilient

Changed from blacklist approach (excluding multiple specific properties) to
only excluding payload. This makes the function more resilient to:

- Future Node-RED properties (will automatically pass through)
- Standard Node-RED properties like topic, _msgid (now preserved)
- Custom user properties (all preserved except payload)

The output message explicitly sets workflowId and payload, so those values
are always controlled regardless of what comes through in passthrough props.

This approach is simpler, more maintainable, and prevents future issues if
Node-RED adds new internal properties.

All 168 tests passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: FriederikeHanssen

nodes/workflow-monitor.js

@@ -65,9 +65,11 @@ module.exports = function (RED) {
       return RED.util.evaluateNodeProperty(p, t, node, msg);
     };
 
-    // Helper to extract passthrough properties from message (excludes standard Node-RED properties)
+    // Helper to extract passthrough properties from message (excludes only payload to prevent memory leaks)
+    // Standard Node-RED properties like topic, _msgid pass through
+    // Output-specific properties like workflowId are explicitly set in output message
     const extractPassthroughProps = (msg) => {
-      const { payload, topic, _msgid, workflowId, workspaceId, ...passthrough } = msg;
+      const { payload, ...passthrough } = msg;
       return passthrough;
     };