fix(后端)：@Transactional + WebMvcProdConfig OPTIONS 跳过

- WebMvcProdConfig：SaInterceptor 增加 OPTIONS 预检跳过，
  解决生产环境 CORS 预检 401 问题
- StudySessionsServiceImpl.endedStudySession/continueStudySession：
  增加 @Transactional
- StudyReportFragmentsServiceImpl.createFragments：
  增加 @Transactional

src/main/java/com/guo/learningprogresstracker/config/WebMvcProdConfig.java

@@ -1,5 +1,6 @@
 package com.guo.learningprogresstracker.config;
 
+import cn.dev33.satoken.context.SaHolder;
 import cn.dev33.satoken.interceptor.SaInterceptor;
 import cn.dev33.satoken.stp.StpUtil;
 import lombok.RequiredArgsConstructor;
@@ -32,7 +33,12 @@ public class WebMvcProdConfig implements WebMvcConfigurer {
 
     @Override
     public void addInterceptors(InterceptorRegistry registry) {
-        registry.addInterceptor(new SaInterceptor(handle -> StpUtil.checkLogin()))
+        registry.addInterceptor(new SaInterceptor(handle -> {
+                    if ("OPTIONS".equalsIgnoreCase(SaHolder.getRequest().getMethod())) {
+                        return;
+                    }
+                    StpUtil.checkLogin();
+                }))
                 .addPathPatterns("/**")
                 .excludePathPatterns("/login");
     }