feat: 改版阶段 1：统一顶栏和教学侧栏、配色和图标规范、路由角色守卫

- 所有页面共用顶栏（教程 / 挑战 / 自由创作 / 作品展，右边“教学”和用户菜单）；
  没登录时顶栏有“登录”按钮，关掉登录框不再白屏；/submission/:id 全屏页不带顶栏
- 后台改成“教学”侧栏，分出题 / 班级 / 管理三组；“全部提交”留在侧栏里打开；
  admin 也能进作品展管理（后端本来就允许）
- 路由按角色守卫：meta.role 为 staff / super，学生和 admin 进不了无权页面
- 配色只在 theme.ts 定义，同时生成 --wp-* CSS 变量和 Naive UI 主题，暗色值先定好
- 图标改用打包进来的 lucide（断网也能显示），去掉 @iconify/vue 和 PUBLIC_ICONIFY_URL；
  代码字体换成打包的 JetBrains Mono，编辑器默认字号 24 → 16
- 教程面板去掉和顶栏重复的切换和图标按钮，图标按钮都补上文字或提示

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

client/src/App.vue

@@ -1,32 +1,17 @@
 <script setup lang="ts">
 import { dateZhCN, zhCN } from "naive-ui"
-import type { GlobalThemeOverrides } from "naive-ui"
 import Login from "./components/Login.vue"
+import AppShell from "./components/layout/AppShell.vue"
 import { onMounted } from "vue"
-import { Account } from "./api"
-import { user } from "./store/user"
+import { useRoute } from "vue-router"
+import { loadUser } from "./store/session"
+import { light, naiveOverrides } from "./theme"
 import hljs from "highlight.js/lib/core"
 
-const themeOverrides: GlobalThemeOverrides = {
-  common: {
-    borderRadius: "6px",
-    borderRadiusSmall: "4px",
-  },
-  Card: {
-    borderRadius: "8px",
-  },
-}
+const route = useRoute()
+const themeOverrides = naiveOverrides(light)
 
-onMounted(async () => {
-  try {
-    const data = await Account.getMyProfile()
-    user.loaded = true
-    user.username = data.username
-    user.role = data.role
-  } catch {
-    user.loaded = true
-  }
-})
+onMounted(loadUser)
 </script>
 
 <template>
@@ -40,7 +25,9 @@ onMounted(async () => {
     <n-modal-provider>
       <n-message-provider :max="1">
         <n-dialog-provider>
-          <router-view></router-view>
+          <!-- 全屏预览这类页面不要顶栏 -->
+          <router-view v-if="route.meta.bare" />
+          <AppShell v-else />
           <Login />
         </n-dialog-provider>
       </n-message-provider>