fix: Persist uploaded image across interactions to keep visualization visible

Problem: Visualization panel was empty after initial analysis because the
uploaded image path wasn't persisted across multiple chat interactions.

Solution:
- Added gr.State to track current_image across interactions
- When no visualization is generated (e.g., grounding fails), show the
uploaded image as a fallback reference
- Image now stays visible throughout the conversation until replaced

This ensures users can always see their uploaded X-ray as reference.

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

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

app.py

@@ -309,10 +309,17 @@ with gr.Blocks() as demo:
         with gr.Column(scale=1):
             viz_output = gr.Image(label="Visualization", height=600)
 
-    def respond(message, chat_history, mode_selection):
+    # State to persist the uploaded image across interactions
+    current_image_state = gr.State(None)
+
+    def respond(message, chat_history, mode_selection, current_image):
         # Convert mode selection to internal mode string
         mode = "socratic" if mode_selection == "Tutor Mode" else "assistant"
 
+        # Track uploaded image - update state when new image is uploaded
+        if isinstance(message, dict) and message.get("files"):
+            current_image = message["files"][0]
+
         # Get response and visualization with mode
         bot_message, viz_image = chat(message, chat_history, mode)
 
@@ -332,9 +339,13 @@ with gr.Blocks() as demo:
         chat_history.append({"role": "user", "content": user_text})
         chat_history.append({"role": "assistant", "content": bot_message})
 
-        return "", chat_history, viz_image
+        # If no visualization was generated, show the current uploaded image as reference
+        if viz_image is None and current_image is not None:
+            viz_image = current_image
+
+        return "", chat_history, viz_image, current_image
 
-    msg.submit(respond, [msg, chatbot, mode_toggle], [msg, chatbot, viz_output])
+    msg.submit(respond, [msg, chatbot, mode_toggle, current_image_state], [msg, chatbot, viz_output, current_image_state])
 
     gr.Examples(
         examples=[