refactor: 后端从 Django 换成 Bun + SQLite

Django 多个 worker 内存占用 1-2 GB，换成 Bun 单进程后约 25 MB，
同时去掉 Postgres 和 Redis，只剩 Caddy + Bun 两个容器。

- server/：Hono + bun:sqlite + Bun 原生 WebSocket，接口与原 django-ninja
  保持兼容；表结构、时间/UUID 存储格式、密码哈希与 Django 一致，旧数据可直接使用
- 评分加权、贝叶斯平滑、成绩册的计算结果与原实现逐位一致（复刻 Python round/sum）
- scripts/：Postgres → SQLite 迁移、新建超管、提示词层级标注、重算分数
- 前端：Django Admin 去掉后，用户新建/修改改为页面内弹窗；
  非超管的挑战公开按钮置灰
- 权限不足返回 JSON 403（原来是重定向到不存在的登录页）
- docker-compose / Caddyfile / dev.sh / CLAUDE.md 更新，删除 AGENTS.md
- 服务器切换步骤见 docs/migrate-to-bun.md

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

client/src/components/editor/Toolbar.vue

@@ -29,20 +29,13 @@
 <script lang="ts" setup>
 import { computed, h } from "vue"
 import { Icon } from "@iconify/vue"
-import {
-  authed,
-  roleAdmin,
-  roleNormal,
-  roleSuper,
-  user,
-} from "../../store/user"
+import { authed, roleAdmin, roleNormal, user } from "../../store/user"
 import { loginModal } from "../../store/modal"
 import { show, panelSize } from "../../store/panel"
 import { taskId } from "../../store/task"
 import { Account } from "../../api"
 import { Role } from "../../utils/type"
 import { router } from "../../router"
-import { ADMIN_URL } from "../../utils/const"
 
 const props = defineProps<{
   submitLoading: boolean
@@ -64,16 +57,6 @@ const menu = computed(() => [
         width: 20,
       }),
   },
-  {
-    label: "数据管理",
-    key: "admin",
-    show: roleSuper.value,
-    icon: () =>
-      h(Icon, {
-        icon: "skill-icons:django",
-        width: 20,
-      }),
-  },
   {
     label: "我的提交",
     key: "submissions",
@@ -106,9 +89,6 @@ function clickMenu(name: string) {
       router.push({ name: route, params: { display: 0 } })
       break
     }
-    case "admin":
-      window.open(ADMIN_URL)
-      break
     case "submissions":
       router.push({
         name: "submissions",