feat: add logger

ui/flutter/lib/util/log_util.dart

@@ -0,0 +1,11 @@
+import 'dart:io';
+
+import 'package:logger/logger.dart';
+import 'package:logger/src/outputs/file_output.dart';
+
+import 'util.dart';
+
+final logger = Logger(
+  printer: PrettyPrinter(),
+  output: Util.isDesktop() ? FileOutput(file: File('log.txt')) : null,
+);