删除项目列表模块（重复内容）

frontend/src/components/Layout.vue

@@ -25,10 +25,6 @@
             <el-icon><Suitcase /></el-icon>
             <span>项目管理</span>
           </el-menu-item>
-          <el-menu-item index="/studies">
-            <el-icon><List /></el-icon>
-            <span>项目列表</span>
-          </el-menu-item>
         </template>
         
         <template v-if="study.currentStudy">
@@ -136,7 +132,7 @@ import { useAuthStore } from "../store/auth";
 import { useStudyStore } from "../store/study";
 import StudySelector from "./StudySelector.vue";
 import { 
-  Monitor, User, Suitcase, List, House, Timer, UserFilled, 
+  Monitor, User, Suitcase, House, Timer, UserFilled, 
   Warning, InfoFilled, QuestionFilled, Checked, Management, 
   Money, Collection, Memo, ArrowDown, SwitchButton 
 } from "@element-plus/icons-vue";