feat: improve AI dialogue evaluation and capability boundaries

kouyu_english/test/dialogue_task_test.dart

@@ -1,5 +1,6 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:kouyu_english/core/courses/courses.dart';
+import 'package:kouyu_english/core/models.dart';
 
 /// The free "初次见面" scene, which is always open.
 LessonDialogue get meet => sceneById('a0-meet').script;
@@ -40,6 +41,21 @@ void main() {
       }
     });
 
+    test('本地判断区分明确错误和需要 AI 理解的自然表达', () {
+      expect(
+        evaluateDialogueStageLocally(meet, 0, '123 ---'),
+        LocalDialogueVerdict.rejected,
+      );
+      expect(
+        evaluateDialogueStageLocally(meet, 0, 'People call me Shen.'),
+        LocalDialogueVerdict.uncertain,
+      );
+      expect(
+        evaluateDialogueStageLocally(meet, 0, 'My name is Shen.'),
+        LocalDialogueVerdict.accepted,
+      );
+    });
+
     test('跑题回答不再因为关键词沾边而通过', () {
       // 旧实现用 text.contains('it')，下面这些句子全部会被判为完成任务。
       expect(