Fix nsd_subset_toggle: always visible, remove ordering-dependent visibility code

scripts/explorer_app.py

@@ -526,9 +526,6 @@ def _apply_dataset_globals(idx):
     nsd_top_heatmaps   = ds.get('nsd_top_heatmaps')
     nsd_mean_heatmaps  = ds.get('nsd_mean_heatmaps')
     HAS_NSD_SUBSET     = nsd_top_img_idx is not None
-    nsd_subset_toggle.visible = HAS_NSD_SUBSET
-    if not HAS_NSD_SUBSET:
-        nsd_subset_toggle.active = False
     top_heatmaps        = ds.get('top_heatmaps')
     mean_heatmaps       = ds.get('mean_heatmaps')
     p75_heatmaps        = ds.get('p75_heatmaps')
@@ -1577,7 +1574,7 @@ _nsd_clip_embeds = None
 nsd_subset_toggle = Toggle(
     label="NSD Subset (sub01)",
     active=False,
-    visible=False,
+    visible=True,
     width=160,
     button_type="success",
 )