feat(复习): 支持会话维度复习 + 标准导图按会话过滤（后端）

- MindMapNode 新增 sessionNum 字段
- BuiltinMindMapGenerator 生成节点时填充 sessionNum
- MindMapTreeTool.filterBySession() 按会话过滤标准导图
- recallCompare 接受 sessionNum 参数
- ReviewRecallRecordEntity 新增 sessionNum 字段
- Flyway V20260705_1: review_recall_records 加 session_num 列
- 新增 GET /study-sessions/tasks/{taskNum}/sessions 端点

src/main/java/com/guo/learningprogresstracker/service/impl/StudySessionsServiceImpl.java

@@ -5,6 +5,7 @@ import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
 import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
 import com.google.protobuf.ServiceException;
 import com.guo.learningprogresstracker.dto.StudySessionsDto;
+import com.guo.learningprogresstracker.dto.response.SessionBriefVO;
 import com.guo.learningprogresstracker.dto.response.StudySessionResponse;
 import com.guo.learningprogresstracker.entity.StudyReportFragmentsEntity;
 import com.guo.learningprogresstracker.entity.StudyReportsEntity;
@@ -26,6 +27,7 @@ import org.springframework.transaction.annotation.Transactional;
 
 import java.time.LocalDateTime;
 import java.util.ArrayList;
+import java.util.List;
 import java.util.Optional;
 import java.util.stream.Collectors;
 
@@ -225,6 +227,34 @@ public class StudySessionsServiceImpl extends ServiceImpl<StudySessionsMapper, S
         return result;
     }
 
+    // ============ 获取任务会话列表（复习维度选择用） ============
+
+    @Override
+    public List<SessionBriefVO> getTaskSessions(String taskNum) {
+        var sessions = this.list(Wrappers.lambdaQuery(StudySessionsEntity.class)
+                .eq(StudySessionsEntity::getTaskNum, taskNum)
+                .orderByDesc(StudySessionsEntity::getStartTime));
+
+        return sessions.stream().map(s -> {
+            SessionBriefVO vo = new SessionBriefVO();
+            vo.setSessionNum(s.getSessionNum());
+            vo.setStartTime(s.getStartTime() != null ? s.getStartTime().toString() : null);
+            // 查询该会话的预期
+            Optional.ofNullable(studyExpectationsService.getBySessionNum(s.getSessionNum()))
+                    .ifPresent(e -> vo.setExpectation(e.getDescription()));
+            // 统计报告和残片数量
+            long reportCount = studyReportsMapper.selectCount(
+                    Wrappers.lambdaQuery(StudyReportsEntity.class)
+                            .eq(StudyReportsEntity::getSessionNum, s.getSessionNum()));
+            long fragmentCount = studyReportFragmentsMapper.selectCount(
+                    Wrappers.lambdaQuery(StudyReportFragmentsEntity.class)
+                            .eq(StudyReportFragmentsEntity::getSessionNum, s.getSessionNum()));
+            vo.setReportCount((int) reportCount);
+            vo.setFragmentCount((int) fragmentCount);
+            return vo;
+        }).collect(Collectors.toList());
+    }
+
     // ============ 活跃会话查询 ============
 
     /**