Update app.py

app.py

@@ -370,7 +370,7 @@ def render_export_button(phase_key: str) -> None:
         "Sheets to include",
         options=options,
         default=[],
-        placeholder="Choose an option",
+        placeholder="Choose option(s)",
         help="Pick the sheets you want to include in the Excel export.",
         key=f"sheets_{phase_key}",
     )