Fix: set ImageExtension after downloading item images in saveWizard

downloadItemImage() saved files to disk but never updated the DB column,
so items appeared to have no images despite files existing on disk.

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

api/setup/saveWizard.php

@@ -667,6 +667,7 @@ try {
             if (!is_dir($itemsDir)) mkdir($itemsDir, 0755, true);
             if (downloadItemImage($menuItemID, $itemImageUrl, $itemsDir)) {
                 $totalImages++;
+                $pdo->prepare("UPDATE Items SET ImageExtension = 'jpg' WHERE ID = ?")->execute([$menuItemID]);
             }
         }
     }