Update app.py

app.py

@@ -8,6 +8,7 @@
 # - Dataset selector (LVD-1689M / SAT-493M); model dropdown shows only the short name between "dinov3-" and "-pretrain".
 # - Sample URL dropdowns switch between LVD (COCO/Picsum) and SAT (satellite imagery) and auto-fill / clear uploads.
 
+import os
 import io
 import math
 import urllib.request