add prompt preview for debug

app.py

@@ -167,6 +167,7 @@ def chat_response(user_msg, chat_history, system_prompt,
 
         pipe = load_pipeline(model_name)
         prompt = format_conversation(history, enriched, pipe.tokenizer)
+        debug += f"\n\n--- Prompt Preview ---\n```\n{prompt}\n```"
         streamer = TextIteratorStreamer(pipe.tokenizer,
                                         skip_prompt=True,
                                         skip_special_tokens=True)