feat: implement automatic message delivery acknowledgement to trigger real-time double-tick status updates

lib/features/messaging/presentation/providers/messaging_provider.dart

@@ -106,6 +106,10 @@ class MessagingNotifier extends StateNotifier<MessagingState> {
       final isMine = message.senderId == _currentUserId;
       if (isMine) return;
 
+      // Immediately ack delivery to backend so sender's tick goes single → double.
+      // This works regardless of Redis presence state and avoids races on send.
+      _socket.ackMessageReceived(convId, message.id);
+
       currentMessages.insert(0, message);
       final updatedMessages =
           Map<String, List<ChatMessage>>.from(state.messages)