Add visual distinction for subsequence cards with teal border

The subsegment-card CSS class was not being applied to subsequence
expansion items. Add the class conditionally and include the teal
accent CSS rules with a 6px left border.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tab_batch_ng.py

@@ -317,7 +317,8 @@ def _render_sequence_card(i, seq, batch_list, data, file_path, state,
     else:
         label = f'Sequence #{seq_num}'
 
-    with ui.expansion(label, icon='movie').classes('w-full'):
+    exp_classes = 'w-full subsegment-card' if is_subsegment(seq_num) else 'w-full'
+    with ui.expansion(label, icon='movie').classes(exp_classes):
         # --- Action row ---
         with ui.row().classes('w-full q-gutter-sm action-row'):
             # Copy from source