opt.: remove GPTBOX>>> from chat title (#22) (#23)

lib/core/util/chat_title.dart

@@ -1,13 +1,15 @@
 abstract final class ChatTitleUtil {
   static const _maxLen = 20;
 
+  static const userCotentLocator = 'GPTBOX>>>';
+
   static const titlePrompt = '''
-Generate a title for the user content behind `GPTBOX>>>` with requirements: 
+Generate a title for the user content behind `$userCotentLocator` with requirements: 
 0. the language of the generated title should be the same as the user content
 1. <= 10 characters if Chinese, Japanese, Korean, etc.
 2. <= $_maxLen letters if English, German, French, etc.
-3. the title should be meaningful, concise, no additional punctuation and only title itself
-GPTBOX>>>''';
+3. the title should be meaningful, concise, no additional punctuation and only title itself.
+$userCotentLocator''';
 
   static final _punctionsRm = RegExp('[“”]');
 
@@ -16,6 +18,8 @@ GPTBOX>>>''';
     if (title.startsWith('《')) title = title.substring(1);
     if (title.endsWith('》')) title = title.substring(0, title.length - 1);
 
+    title = title.replaceFirst(userCotentLocator, '');
+
     title = title.replaceAll(_punctionsRm, '');
     title = title.replaceAll('\n', ' ');