fix: 修正学习流程中的证据、复习与进度问题

- 独立尝试按课程要求校验内容，不再任意输入即算独立成功
- 复习节点改为学后第 1/3/7/14 天，之后每 30 天抽查；复习轮换情境
- 掌握状态按作答记录推导：需认识、可回忆、跨情境使用及最近两次无帮助
- 课程证据按实际用到的目标记录；跟读与课程对话只算辅助练习
- 复习成功不再降低已有状态
- 学完课程后进入下一节未完成课程；全部学完后引导巩固与阶段评估
- 新增 3 题基础定位，按结果设置起始课程
- 新增按课程开放的对话场景，首页推荐最少练习的场景
- 切换课程时清空上一课的步骤进度
- AI 返回 JSON 格式并按 JSON 回放历史；拼写校验忽略大小写与连字符；移除学习目标选择

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kouyu_english/test/deepseek_thinking_test.dart

@@ -43,6 +43,7 @@ void main() {
     final body = await captureBody('https://api.deepseek.com');
 
     expect(body['thinking'], {'type': 'disabled'});
+    expect(body['response_format'], {'type': 'json_object'});
     expect(body.containsKey('reasoning_effort'), isFalse);
     expect(body['max_tokens'], 200);
   });
@@ -51,6 +52,9 @@ void main() {
     final body = await captureBody('https://api.deepseek.com/v1/responses');
 
     expect(body['reasoning'], {'effort': 'none'});
+    expect(body['text'], {
+      'format': {'type': 'json_object'},
+    });
     expect(body.containsKey('reasoning_effort'), isFalse);
     expect(body.containsKey('thinking'), isFalse);
   });
@@ -59,6 +63,48 @@ void main() {
     final body = await captureBody('https://example.test/v1');
 
     expect(body.containsKey('thinking'), isFalse);
+    expect(body.containsKey('response_format'), isFalse);
     expect(body['reasoning_effort'], 'low');
   });
+
+  test('dialogue history replays earlier AI lines as JSON', () async {
+    AiService.instance.setFallbackApiKey('test-key');
+    List<dynamic>? messages;
+    final reply = await http.runWithClient(
+      () => AiService.instance.dialogueReply(
+        provider: AiProviderType.compatible,
+        endpoint: 'https://api.deepseek.com',
+        model: 'deepseek-flash',
+        aiGoal: 'Ask where the learner is from.',
+        learnerTask: 'say where they are from',
+        history: const [
+          {'role': 'assistant', 'content': "Hi! What's your name?"},
+          {'role': 'user', 'content': 'My name is Alex.'},
+        ],
+      ),
+      () => MockClient((request) async {
+        final body = jsonDecode(request.body) as Map<String, dynamic>;
+        messages = body['messages'] as List<dynamic>;
+        return http.Response(
+          jsonEncode({
+            'choices': [
+              {
+                'message': {'content': '{"reply":"Where are you from?"}'},
+              },
+            ],
+          }),
+          200,
+          headers: {'content-type': 'application/json; charset=utf-8'},
+        );
+      }),
+    );
+
+    expect(reply?.reply, 'Where are you from?');
+    expect(messages, hasLength(3));
+    expect(messages![0]['role'], 'system');
+    expect(jsonDecode(messages![1]['content'] as String), {
+      'reply': "Hi! What's your name?",
+    });
+    expect(messages![2], {'role': 'user', 'content': 'My name is Alex.'});
+  });
 }