feat(复习)：回忆对比优先走 AI 语义对比，失败时降级为内置算法

- CompareResult.java：新增 evaluation 字段（AI 对比时写入评价文本）
- AiServiceClient.java：新增 compareRecall()，调用 lpt-ai /ai/compare-recall
- StandardMindMapServiceImpl.java：recallCompare() 中注入 AiServiceClient，
  优先 try AI 语义对比，含层级上下文和同义表达识别；
  AI 不可用或失败时自动 fallback 到内置标题匹配算法
- StandardMindMapServiceImplTest.java：适配新增的 AiServiceClient 依赖

src/test/java/com/guo/learningprogresstracker/service/impl/StandardMindMapServiceImplTest.java

@@ -45,6 +45,8 @@ class StandardMindMapServiceImplTest {
     private List<MindMapAiClient> aiClients;
     @Mock
     private MindMapAiClient mockAiClient;
+    @Mock
+    private AiServiceClient aiServiceClient;
 
     private final ObjectMapper objectMapper = new ObjectMapper();
 
@@ -189,7 +191,7 @@ class StandardMindMapServiceImplTest {
                 standardMindMapMapper, recallRecordMapper,
                 tasksMapper, studyReportsMapper, studyReportFragmentsMapper,
                 taskApplicationMapper, studySessionsMapper,
-                List.of(mockAiClient), objectMapper);
+                List.of(mockAiClient), objectMapper, aiServiceClient);
         return s;
     }
 }