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>

server/scripts/classify-prompts.ts

@@ -0,0 +1,47 @@
+/**
+ * 用大模型给学生提示词标注布鲁姆认知层级（L1-L6）。
+ *
+ *   bun scripts/classify-prompts.ts [--task-id N] [--force] [--dry-run]
+ *
+ * 默认只处理还没有层级的用户消息；--force 重新标注全部。
+ */
+import { parseArgs } from "node:util"
+import { all } from "../src/db"
+import { classifyMessage } from "../src/services/classifier"
+import { llmConfigured } from "../src/services/llm"
+
+const { values } = parseArgs({
+  options: {
+    "task-id": { type: "string" },
+    force: { type: "boolean", default: false },
+    "dry-run": { type: "boolean", default: false },
+  },
+})
+
+const where = ["m.role = 'user'"]
+const params: Record<string, unknown> = {}
+if (values["task-id"]) {
+  where.push("c.task_id = $task_id")
+  params.task_id = Number(values["task-id"])
+}
+if (!values.force) where.push("m.prompt_level IS NULL")
+
+const ids = all<{ id: number }>(
+  `SELECT m.id FROM prompt_message m JOIN prompt_conversation c ON c.id = m.conversation_id
+   WHERE ${where.join(" AND ")} ORDER BY m.created, m.id`,
+  params,
+).map((r) => r.id)
+
+console.log(`找到 ${ids.length} 条消息需要标注`)
+if (values["dry-run"]) process.exit(0)
+if (!llmConfigured()) {
+  console.error("没有配置 LLM_API_KEY")
+  process.exit(1)
+}
+
+for (const [i, id] of ids.entries()) {
+  const level = await classifyMessage(id)
+  console.log(`[${i + 1}/${ids.length}] msg#${id} → ${level ? `L${level}` : "(跳过)"}`)
+  await Bun.sleep(300)
+}
+console.log("完成")

server/scripts/create-superuser.ts

@@ -0,0 +1,33 @@
+/**
+ * 新建超级管理员，或把已有用户设为超级管理员并重设密码。
+ *
+ *   bun scripts/create-superuser.ts <用户名> <密码>
+ */
+import { get, run, now } from "../src/db"
+import { makePassword } from "../src/auth"
+
+const [username, password] = process.argv.slice(2)
+if (!username || !password) {
+  console.error("用法：bun scripts/create-superuser.ts <用户名> <密码>")
+  process.exit(1)
+}
+
+const hash = await makePassword(password)
+const user = get<{ id: number }>(`SELECT id FROM account_user WHERE username = $username`, { username })
+if (user) {
+  run(
+    `UPDATE account_user SET password = $hash, raw_password = $raw, role = 'super',
+       is_superuser = 1, is_staff = 1, is_active = 1 WHERE id = $id`,
+    { hash, raw: password.slice(0, 20), id: user.id },
+  )
+  run(`DELETE FROM auth_session WHERE user_id = $id`, { id: user.id })
+  console.log(`已将 ${username} 设为超级管理员并重设密码`)
+} else {
+  run(
+    `INSERT INTO account_user
+       (password, last_login, is_superuser, username, email, is_staff, is_active, date_joined, role, raw_password, classname)
+     VALUES ($hash, NULL, 1, $username, '', 1, 1, $now, 'super', $raw, '')`,
+    { hash, username, now: now(), raw: password.slice(0, 20) },
+  )
+  console.log(`已创建超级管理员 ${username}`)
+}

server/scripts/migrate-from-postgres.ts

@@ -0,0 +1,134 @@
+/**
+ * 把旧 Django 项目的 Postgres 数据导入 SQLite（一次性迁移）。
+ *
+ *   POSTGRES_HOST=... POSTGRES_DB=... POSTGRES_USER=... POSTGRES_PASSWORD=... \
+ *     bun scripts/migrate-from-postgres.ts [--force]
+ *
+ * 目标库为 DB_PATH（默认 data/db.sqlite3）。目标库已有数据时需要 --force（会先清空）。
+ * 会话不迁移，所有人需要重新登录一次。
+ */
+import { SQL } from "bun"
+import { config } from "../src/config"
+import { db } from "../src/db"
+
+// 按外键依赖顺序
+const TABLES = [
+  "account_user",
+  "task_task",
+  "task_tutorial",
+  "task_challenge",
+  "task_creation",
+  "task_taskasset",
+  "submission_submission",
+  "submission_rating",
+  "submission_award",
+  "submission_submissionaward",
+  "prompt_conversation",
+  "prompt_message",
+]
+
+const force = process.argv.includes("--force")
+const env = process.env
+for (const key of ["POSTGRES_HOST", "POSTGRES_DB", "POSTGRES_USER", "POSTGRES_PASSWORD"]) {
+  if (!env[key]) {
+    console.error(`缺少环境变量 ${key}`)
+    process.exit(1)
+  }
+}
+
+const pg = new SQL({
+  hostname: env.POSTGRES_HOST,
+  port: Number(env.POSTGRES_PORT ?? 5432),
+  database: env.POSTGRES_DB,
+  username: env.POSTGRES_USER,
+  password: env.POSTGRES_PASSWORD,
+})
+
+const existing = db.query(`SELECT COUNT(*) AS n FROM account_user`).get() as { n: number }
+if (existing.n > 0 && !force) {
+  console.error(`目标库 ${config.dbPath} 已有数据，加 --force 会清空后重新导入`)
+  process.exit(1)
+}
+
+const quote = (name: string) => `"${name.replaceAll('"', '""')}"`
+
+// 按 Postgres 的列类型转换成 Django 在 SQLite 中的存储格式
+function selectExpr(column: string, pgType: string) {
+  const c = quote(column)
+  switch (pgType) {
+    case "timestamp with time zone":
+      return `to_char(${c} AT TIME ZONE 'UTC', 'YYYY-MM-DD HH24:MI:SS.US') AS ${c}`
+    case "timestamp without time zone":
+      return `to_char(${c}, 'YYYY-MM-DD HH24:MI:SS.US') AS ${c}`
+    case "uuid":
+      return `replace(${c}::text, '-', '') AS ${c}`
+    case "boolean":
+      return `${c}::int AS ${c}`
+    case "bigint":
+      return `${c}::text AS ${c}`
+    default:
+      return c
+  }
+}
+
+const counts: Record<string, number> = {}
+const rowsByTable: Record<string, Record<string, unknown>[]> = {}
+
+for (const table of TABLES) {
+  const sqliteColumns = (db.query(`PRAGMA table_info(${quote(table)})`).all() as { name: string }[]).map(
+    (c) => c.name,
+  )
+  const pgColumns = await pg`
+    SELECT column_name, data_type FROM information_schema.columns
+    WHERE table_schema = 'public' AND table_name = ${table}`
+  if (!pgColumns.length) throw new Error(`Postgres 中没有表 ${table}`)
+  const pgTypes = new Map<string, string>(pgColumns.map((c: any) => [c.column_name, c.data_type]))
+  const missing = sqliteColumns.filter((c) => !pgTypes.has(c))
+  if (missing.length) throw new Error(`Postgres 表 ${table} 缺少列：${missing.join(", ")}`)
+
+  const select = sqliteColumns.map((c) => selectExpr(c, pgTypes.get(c)!)).join(", ")
+  const rows: Record<string, unknown>[] = await pg.unsafe(`SELECT ${select} FROM ${quote(table)}`)
+  for (const row of rows) {
+    for (const c of sqliteColumns) {
+      if (pgTypes.get(c) === "bigint" && row[c] !== null) row[c] = Number(row[c])
+    }
+  }
+  rowsByTable[table] = rows
+  console.log(`读取 ${table}: ${rows.length} 行`)
+}
+await pg.close()
+
+db.transaction(() => {
+  db.run("PRAGMA defer_foreign_keys = ON")
+  for (const table of [...TABLES].reverse()) db.run(`DELETE FROM ${quote(table)}`)
+  db.run(`DELETE FROM auth_session`)
+  for (const table of TABLES) {
+    const rows = rowsByTable[table]!
+    if (!rows.length) {
+      counts[table] = 0
+      continue
+    }
+    const columns = Object.keys(rows[0]!)
+    const insert = db.prepare(
+      `INSERT INTO ${quote(table)} (${columns.map(quote).join(", ")})
+       VALUES (${columns.map((c) => "$" + c).join(", ")})`,
+    )
+    for (const row of rows) insert.run(row as any)
+    counts[table] = rows.length
+  }
+})()
+
+// 校验
+let ok = true
+for (const table of TABLES) {
+  const n = (db.query(`SELECT COUNT(*) AS n FROM ${quote(table)}`).get() as { n: number }).n
+  if (n !== counts[table]) ok = false
+  console.log(`${n === counts[table] ? "✓" : "✗"} ${table}: ${n}`)
+}
+const fk = db.query(`PRAGMA foreign_key_check`).all()
+if (fk.length) {
+  ok = false
+  console.error("外键检查失败：", fk.slice(0, 10))
+}
+console.log(ok ? `\n导入完成：${config.dbPath}` : "\n导入有问题，请检查上面的输出")
+process.exit(ok ? 0 : 1)

server/scripts/recalculate-scores.ts

@@ -0,0 +1,28 @@
+/**
+ * 重新计算所有被评过分的提交的 score / raw_score / zone（修改评分规则后使用）。
+ *
+ *   bun scripts/recalculate-scores.ts [--dry-run]
+ */
+import { all, get } from "../src/db"
+import { updateSubmissionScore } from "../src/services/score"
+
+const rows = all<{ id: string; username: string; title: string; score: number }>(
+  `SELECT s.id, u.username, t.title, s.score FROM submission_submission s
+   JOIN account_user u ON u.id = s.user_id JOIN task_task t ON t.id = s.task_id
+   WHERE EXISTS (SELECT 1 FROM submission_rating r WHERE r.submission_id = s.id)
+   ORDER BY s.created DESC`,
+)
+console.log(`找到 ${rows.length} 个被评过分的提交`)
+if (process.argv.includes("--dry-run")) process.exit(0)
+
+for (const [i, s] of rows.entries()) {
+  updateSubmissionScore(s.id)
+  const after = get<{ score: number; zone: string | null }>(
+    `SELECT score, zone FROM submission_submission WHERE id = $id`,
+    { id: s.id },
+  )!
+  console.log(
+    `[${i + 1}/${rows.length}] ${s.username}/${s.title}: ${s.score.toFixed(3)} → ${after.score.toFixed(3)}  zone=${after.zone}`,
+  )
+}
+console.log("完成")