refactor(download): remove ProviderCore/download.py, move sanitize_filename to SYS.utils, replace callers to use API.HTTP.HTTPClient

cmdlet/add_file.py

@@ -321,9 +321,11 @@ class Add_File(Cmdlet):
         is_storage_backend_location = False
         if location:
             try:
-                store_probe = Store(config)
+                # Use a config-only check to avoid instantiating backends (which may perform network checks).
+                from Store.registry import list_configured_backend_names
+
                 is_storage_backend_location = location in (
-                    store_probe.list_backends() or []
+                    list_configured_backend_names(config) or []
                 )
             except Exception:
                 is_storage_backend_location = False