Auto-populate columns on file upload, remove redundant button

app.py

@@ -276,13 +276,11 @@ https://github.com/chrissoria/cat-llm
                 file_types=[".csv", ".xlsx", ".xls"]
             )
 
-            with gr.Row():
-                spreadsheet_column = gr.Dropdown(
-                    label="Column to Classify",
-                    choices=[],
-                    info="Select the column containing text to classify"
-                )
-                load_cols_btn = gr.Button("Upload File", size="sm")
+            spreadsheet_column = gr.Dropdown(
+                label="Column to Classify",
+                choices=[],
+                info="Select the column containing text to classify"
+            )
 
             gr.Markdown("### Categories")
             category_inputs = []
@@ -365,7 +363,7 @@ https://github.com/chrissoria/cat-llm
         outputs=[model, api_key, api_key_status]
     )
 
-    load_cols_btn.click(
+    spreadsheet_file.change(
         fn=load_columns,
         inputs=[spreadsheet_file],
         outputs=[spreadsheet_column, status]