fixed stalled requests after app resume

lib/api/marianumconnect/marianumconnect_api.dart

@@ -16,6 +16,16 @@ class MarianumConnectApi {
 
   static Dio dio() => _instance;
 
+  /// Drops the pooled keep-alive sockets. After a suspend the OS or a NAT
+  /// has usually killed them already, but dart:io only notices once a request
+  /// is written into one — which then hangs until [_receiveTimeout].
+  /// In-flight requests finish on the old adapter.
+  static void resetConnections() {
+    final stale = _instance.httpClientAdapter;
+    _instance.httpClientAdapter = HttpClientAdapter();
+    stale.close();
+  }
+
   /// A fresh dio with the standard JSON options but no interceptors — used by
   /// the auth queries (login/verify) that must bypass the bearer/demo
   /// interceptors to avoid a re-auth loop.