Fix dataframe CSV download functionality

- Simplified st.dataframe to use built-in download feature properly
- Added hide_index=True parameter to enable CSV download button
- Removed custom download implementation in favor of native functionality

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

Co-Authored-By: Claude <[email protected]>

app.py

@@ -481,21 +481,12 @@ def show_custom_response(response):
             </div>
             """, unsafe_allow_html=True)
             
-            # Display dataframe with download option
-            st.dataframe(content, use_container_width=True)
-            
-            # Add download button for CSV
-            import io
-            csv_buffer = io.StringIO()
-            content.to_csv(csv_buffer, index=False)
-            csv_data = csv_buffer.getvalue()
-            
-            st.download_button(
-                label="📥 Download as CSV",
-                data=csv_data,
-                file_name=f"vayuchat_data_{datetime.now().strftime('%Y%m%d_%H%M%S')}.csv",
-                mime="text/csv",
-                use_container_width=True
+            # Display dataframe with built-in download functionality
+            st.dataframe(
+                content, 
+                use_container_width=True,
+                hide_index=True,
+                column_config=None
             )
         
         # Show generated code with Streamlit expander