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/dashboard/UserActions.vue

@@ -19,13 +19,19 @@
     >
       解封
     </n-button>
+    <UserFormModal
+      v-model:show="showEdit"
+      :user="user"
+      @saved="emits('reload')"
+    />
   </n-flex>
 </template>
 <script lang="ts" setup>
+import { ref } from "vue"
 import { useMessage } from "naive-ui"
 import { Account } from "../../api"
-import { ADMIN_URL } from "../../utils/const"
 import { Role, type User } from "../../utils/type"
+import UserFormModal from "./UserFormModal.vue"
 
 interface Props {
   user: User
@@ -35,9 +41,10 @@ const props = defineProps<Props>()
 const emits = defineEmits(["reload"])
 
 const message = useMessage()
+const showEdit = ref(false)
 
 function edit() {
-  window.open(`${ADMIN_URL}/account/user/${props.user.id}/change/`)
+  showEdit.value = true
 }
 
 async function toggleUserActive() {

client/src/components/dashboard/UserFormModal.vue

@@ -0,0 +1,95 @@
+<template>
+  <n-modal
+    style="width: 360px"
+    :mask-closable="false"
+    preset="card"
+    :title="user ? `修改 ${user.username}` : '新建用户'"
+    :show="show"
+    @update:show="emit('update:show', $event)"
+  >
+    <n-form label-placement="left" label-width="60">
+      <n-form-item label="用户名">
+        <n-input v-model:value="form.username" />
+      </n-form-item>
+      <n-form-item label="密码">
+        <n-input
+          v-model:value="form.password"
+          :placeholder="user ? '不修改请留空' : '6 到 20 位'"
+        />
+      </n-form-item>
+      <n-form-item label="权限">
+        <n-select v-model:value="form.role" :options="roles" />
+      </n-form-item>
+      <n-form-item label="班级">
+        <n-input v-model:value="form.classname" placeholder="可不填" />
+      </n-form-item>
+    </n-form>
+    <n-button
+      type="primary"
+      block
+      :loading="loading"
+      :disabled="!form.username || (!user && !form.password)"
+      @click="submit"
+    >
+      保存
+    </n-button>
+  </n-modal>
+</template>
+<script lang="ts" setup>
+import { reactive, ref, watch } from "vue"
+import { useMessage } from "naive-ui"
+import { Account } from "../../api"
+import { Role, type User } from "../../utils/type"
+
+const props = defineProps<{ show: boolean; user?: User | null }>()
+const emit = defineEmits(["update:show", "saved"])
+
+const message = useMessage()
+const loading = ref(false)
+const form = reactive({
+  username: "",
+  password: "",
+  role: Role.Normal,
+  classname: "",
+})
+
+const roles = [
+  { label: "普通用户", value: Role.Normal },
+  { label: "管理员", value: Role.Admin },
+]
+
+watch(
+  () => props.show,
+  (show) => {
+    if (!show) return
+    form.username = props.user?.username ?? ""
+    form.password = ""
+    form.role = props.user?.role ?? Role.Normal
+    form.classname = props.user?.classname ?? ""
+  },
+)
+
+async function submit() {
+  loading.value = true
+  try {
+    const data = props.user
+      ? await Account.update(props.user.id, {
+          username: form.username,
+          role: form.role,
+          classname: form.classname,
+          ...(form.password ? { password: form.password } : {}),
+        })
+      : await Account.create({ ...form })
+    message.success(data.message)
+    emit("update:show", false)
+    emit("saved")
+  } catch (err: any) {
+    const detail = err.response?.data?.detail
+    message.error(
+      typeof detail === "string" ? detail : (detail?.[0]?.msg ?? "保存失败"),
+    )
+  } finally {
+    loading.value = false
+  }
+}
+</script>