Fix: serialize structured_data and trace as JSON strings in dataset traces

app.py

@@ -208,8 +208,8 @@ def _push_trace(question: str, answer: str, trace: list, structured_data=None) -
             "timestamp":      datetime.datetime.utcnow().isoformat() + "Z",
             "question":       question,
             "answer":         answer,
-            "structured_data": structured_data,
-            "trace":          trace,
+            "structured_data": json.dumps(structured_data) if structured_data else None,
+            "trace":          json.dumps(trace),
             "model":          "Qwen2.5-3B-Instruct (llama.cpp Q4_K_M)",
         }
         fname = f"traces/trace_{datetime.datetime.utcnow().strftime('%Y%m%d_%H%M%S_%f')}.json"