[Flutter] Force a username before subscribing

flutter/lib/pages/channel_scanner/channel_scanner_result_channelsubscribe.dart

@@ -12,6 +12,7 @@ import 'package:simplecloudnotifier/state/app_auth.dart';
 import 'package:simplecloudnotifier/state/application_log.dart';
 import 'package:simplecloudnotifier/utils/navi.dart';
 import 'package:simplecloudnotifier/utils/toaster.dart';
+import 'package:simplecloudnotifier/utils/dialogs.dart';
 import 'package:simplecloudnotifier/utils/ui.dart';
 
 class ChannelScannerResultChannelSubscribe extends StatefulWidget {
@@ -172,6 +173,38 @@ class _ChannelScannerResultChannelSubscribeState extends State<ChannelScannerRes
 
   void _onSubscribe() async {
     final auth = Provider.of<AppAuth>(context, listen: false);
+
+    // Check if username is set
+    try {
+      final user = await auth.loadUser();
+      if (user.username == null || user.username!.isEmpty) {
+        // Show modal to set username
+        var newusername = await UIDialogs.showUsernameRequiredDialog(context);
+
+        if (newusername == null) return; // User cancelled
+
+        newusername = newusername.trim();
+        if (newusername.isEmpty) {
+          Toaster.error("Error", 'Username cannot be empty');
+          return;
+        }
+
+        // Update username via API
+        try {
+          await APIClient.updateUser(auth, auth.userID!, username: newusername);
+          await auth.loadUser(force: true); // Refresh cached user
+          Toaster.success("Success", 'Username set');
+        } catch (e) {
+          Toaster.error("Error", 'Failed to set username: ${e.toString()}');
+          return;
+        }
+      }
+    } catch (e) {
+      Toaster.error("Error", 'Failed to load user data: ${e.toString()}');
+      return;
+    }
+
+    // Proceed with subscription
     try {
       var sub = await APIClient.subscribeToChannelbyID(auth, widget.value.channelID, subscribeKey: widget.value.subscribeKey);
       if (sub.confirmed) {