Share sheet: Hidden and Storage toggles, plus diagnostics for the missing accounts

Two menu chips start at the account's app settings (hidden filter, storage
scope - now published per account), hidden-on asks for the app's unlock, and
external storage is detected via nc:mount-type incl. everything under a
mount. Adds logging for which accounts get published and why one is skipped.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

lib/providers/files_controller.dart

@@ -677,6 +677,19 @@ class FilesController extends ChangeNotifier
     );
   }
 
+  /// The storage scope saved for [accountId] (see [savedHiddenFilter]).
+  static StorageScope savedStorageScope(
+    SharedPreferences prefs,
+    String Function(String accountId, String baseKey) accountPrefKey,
+    String accountId,
+  ) {
+    final name = prefs.getString(accountPrefKey(accountId, _prefStorageScope));
+    return StorageScope.values.firstWhere(
+      (s) => s.name == name,
+      orElse: () => StorageScope.cloud,
+    );
+  }
+
   /// The hidden-files filter saved for [accountId] - not just the active
   /// account's, which is all [hiddenFilter] holds. For iOS's Share Extension,
   /// which follows each account's own setting.