test(rag_phase4): handle None status before .lower() in error check

tests/test_rag_phase4_final_verify.py

@@ -75,7 +75,7 @@ def test_phase4_final_verify(live_gui):
    if status == 'done':
     success = True
     break
-   if "error" in status.lower():
+   if status and "error" in status.lower():
     print(f"[VERIFY] Error detected: {status}")
     break
    time.sleep(0.5)