Add: dummy backend for behavioural testing

docs/QA_WORKFLOW.md

@@ -72,6 +72,12 @@ cargo test --workspace
 just qa-validate
 ```
 
+Optional runtime/API stress validation:
+
+```powershell
+just random-backend-test
+```
+
 For runtime behavior issues, include screenshot capture paths in the issue file.
 
 ## Definition of Done