Fix DM private media sending

lib/widgets/messages/transfer_timeout.dart

@@ -0,0 +1,24 @@
+import 'dart:async';
+
+/// Calculates a transfer timeout as 2× the estimated LoRa airtime,
+/// with a minimum of 30 seconds.
+///
+/// Used by [ImageMessageBubble] and [VoiceMessageBubble] to reset the
+/// "loading" spinner when a transfer stalls, allowing the user to retry.
+class TransferTimeout {
+  static const Duration _minimum = Duration(seconds: 30);
+
+  /// Start a one-shot timer based on [txEstimate] × 2 (min 30s).
+  ///
+  /// [onTimeout] is called on the UI thread when the timer fires.
+  /// Returns the [Timer] so the caller can cancel it (e.g. on dispose or
+  /// when the transfer completes).
+  static Timer start({
+    required Duration txEstimate,
+    required void Function() onTimeout,
+  }) {
+    final timeout = txEstimate * 2;
+    final effective = timeout < _minimum ? _minimum : timeout;
+    return Timer(effective, onTimeout);
+  }
+}