feat：重构倒计时相关内容，将倒计时逻辑放在后端进行

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

@@ -1,6 +1,7 @@
 package com.guo.learningprogresstracker.controller;
 
 import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
+import com.google.protobuf.ServiceException;
 import com.guo.learningprogresstracker.common.Ops;
 import com.guo.learningprogresstracker.dto.TaskInfo;
 import com.guo.learningprogresstracker.dto.response.StudySessionResponse;
@@ -80,7 +81,7 @@ public class TaskController {
      */
     @GetMapping("/{taskNum}/study-sessions/start-or-continue")
     public CommonResult<StudySessionResponse> startOrContinueStudySession(@NotEmpty(message = "taskNum不可为空")
-                                                                          @PathVariable String taskNum) throws NotFindEntitiesException {
+                                                                          @PathVariable String taskNum) throws NotFindEntitiesException, ServiceException {
         StudySessionResponse response = studySessionsServiceImpl.startOrContinueStudySession(taskNum);
         return CommonResult.success(response);