新增空闲锁屏、修复401等问题，新增文件版本管理、共享库等占位符

frontend/src/App.vue

@@ -1,4 +1,27 @@
 <template>
-  <router-view />
+  <div class="app-shell" :class="{ 'app-locked': session.locked }">
+    <router-view />
+    <LockScreenModal v-if="session.locked" />
+  </div>
   <!-- TODO: 预留聚合接口页面：/study/{id}/overview /subjects/{id}/detail /sites/{id}/summary -->
 </template>
+
+<script setup lang="ts">
+import { useSessionStore } from "./store/session";
+import { initSessionManager } from "./session/sessionManager";
+import LockScreenModal from "./components/LockScreenModal.vue";
+
+initSessionManager();
+const session = useSessionStore();
+</script>
+
+<style scoped>
+.app-shell {
+  min-height: 100vh;
+}
+
+.app-locked {
+  pointer-events: none;
+  user-select: none;
+}
+</style>