feat(复习): 节点级 focusPath + findNode，回退 session 维度

- 移除 MindMapNode.sessionNum、filterBySession、getTaskSessions
- 新增 MindMapTreeTool.extractSubtree() 按路径提取子树作为对比基准
- 新增 findClosestNode/getPath/similarityScore 支持节点匹配
- 新增 POST /review/standard-mind-map/{taskNum}/find-node
- recallCompare 使用 focusPath 替代 sessionNum
- ReviewRecallRecordEntity.focusPath 替代 sessionNum
- Flyway V20260706_1: review_recall_records 加 focus_path 列

src/main/java/com/guo/learningprogresstracker/controller/StudySessionController.java

@@ -18,9 +18,7 @@ import lombok.RequiredArgsConstructor;
 import org.springframework.validation.annotation.Validated;
 import org.springframework.web.bind.annotation.*;
 
-import com.guo.learningprogresstracker.dto.response.SessionBriefVO;
 import java.util.ArrayList;
-import java.util.List;
 import java.time.LocalDateTime;
 
 /**
@@ -139,10 +137,4 @@ public class StudySessionController {
             @RequestParam(required = false) String excludeTaskNum) {
         return CommonResult.success(studySessionsServiceImpl.getActiveSession(excludeTaskNum));
     }
-
-    /** 获取任务的所有会话简要列表（用于复习维度选择） */
-    @GetMapping("/tasks/{taskNum}/sessions")
-    public CommonResult<List<SessionBriefVO>> getTaskSessions(@PathVariable String taskNum) {
-        return CommonResult.success(studySessionsServiceImpl.getTaskSessions(taskNum));
-    }
 }