Update default category

src/streamlit_app.py

@@ -280,10 +280,11 @@ with st.sidebar:
 
     target_mode = st.selectbox("Target category mode", ["Pick specific", "Random each time"], index=0)
     if target_mode == "Pick specific":
+        cats = st.session_state.categories if st.session_state.categories else ["(load TSV first)"]
 
         DEFAULT_CAT = "bus"  # normalized label
 
-        if cats and DEFAULT_CAT in st.session_state.categories:
+        if cats and DEFAULT_CAT in cats:
             default_idx = cats.index(DEFAULT_CAT)
         else:
             default_idx = 0  # fallback