feat(历史报告): 展示学习预期目标以区分各会话

StudyReportsEntity 新增 sessionExpectation 字段（非数据库），
getTaskReports() 查询后自动填充对应会话的预期描述，
前端报告条目显示 sessionNum + 预期目标。

src/main/java/com/guo/learningprogresstracker/entity/StudyReportsEntity.java

@@ -33,6 +33,11 @@ public class StudyReportsEntity extends BaseEntity implements Serializable {
     @TableField(value = "content")
     private String content;
 
+    /**
+     * 对应学习会话的预期目标（非数据库字段，查询时填充）
+     */
+    @TableField(exist = false)
+    private String sessionExpectation;
 
     @TableField(exist = false)
     private static final long serialVersionUID = 1L;

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

@@ -214,7 +214,15 @@ public class StudySessionsServiceImpl extends ServiceImpl<StudySessionsMapper, S
         if (keyword != null && !keyword.isBlank()) {
             wrapper.like(StudyReportsEntity::getContent, keyword);
         }
-        return studyReportsMapper.selectPage(pg, wrapper);
+        Page<StudyReportsEntity> result = studyReportsMapper.selectPage(pg, wrapper);
+        // 填充每个报告对应会话的预期目标
+        for (StudyReportsEntity report : result.getRecords()) {
+            if (report.getSessionNum() != null) {
+                Optional.ofNullable(studyExpectationsService.getBySessionNum(report.getSessionNum()))
+                        .ifPresent(e -> report.setSessionExpectation(e.getDescription()));
+            }
+        }
+        return result;
     }
 
     // ============ 活跃会话查询 ============