Fix chat export formatting and f-string syntax

app.py

@@ -503,8 +503,13 @@ async def serve(q: Q):
                 prefix = "User: " if msg[1] else "Response: "
                 chat_history.append(f'{prefix}{msg[0]}')
             
+            # Create formatted chat history text
+            chat_history_text = '\n'.join(chat_history)
+
+            # Create full export content
             export_content = f'''YouTube Video Transcript Chatbot
-Transcript:
+            
+    Transcript:
 {q.client.transcript}
 
 Chat History: