Indent xml for saving

lib/mod_list.dart

@@ -257,8 +257,15 @@ class ModList {
       // Build the XML document
       final xmlDocument = builder.buildDocument();
 
-      // Write the XML document to file
-      file.writeAsStringSync(xmlDocument.toString());
+      // Convert to string with 2-space indentation
+      final prettyXml = xmlDocument.toXmlString(
+        pretty: true, 
+        indent: '  ', // 2 spaces
+        newLine: '\n',
+      );
+
+      // Write the formatted XML document to file
+      file.writeAsStringSync(prettyXml);
       logger.info('Successfully saved mod configuration to: $configPath');
     } catch (e) {
       logger.error('Error saving configuration file: $e');