Fix Gradio messages format based on official documentation

Issue: Gradio msg.submit automatically adds user message to history
Solution: Only append assistant response, not both user and assistant

Based on Gradio 5 official docs for type="messages":
- msg.submit automatically handles adding user message
- Response function should only append assistant's reply
- Format: {"role": "assistant", "content": bot_message}

Fixes: "Data incompatible with messages format" error

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

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

app.py

@@ -188,18 +188,12 @@ with gr.Blocks() as demo:
         # Get response and visualization
         bot_message, viz_image = chat(message, chat_history)
 
-        # Extract text from message
-        if isinstance(message, dict):
-            text = message.get("text", "")
-        else:
-            text = message
-
-        # Add to chat history - use messages format for newer Gradio
+        # Initialize chat history if None
         if chat_history is None:
             chat_history = []
 
-        # Use dict format with role/content for messages type chatbot
-        chat_history.append({"role": "user", "content": text})
+        # Gradio automatically adds the user message when using msg.submit
+        # We only need to append the assistant's response in messages format
         chat_history.append({"role": "assistant", "content": bot_message})
 
         return "", chat_history, viz_image