feat(阶段3): oj 侧端点铺开（基线提交，未经评审）

由外部 agent (Codex) 在本会话额度中断期间完成。原样提交作为基线，
后续修复单独成 commit，便于区分与回退。

覆盖 oj 侧 65 个端点，新增 9 组路由（account/achievement/ai/classroom/
content/contest/flowchart/problemset/site）与对应 Zod 契约。

已核验：tsc --noEmit 退出码 0；API 可启动；/api/problems 返回真实数据；
judge 与 flowchart worker 均 ready。
未核验：权限边界与数据泄露，评审进行中。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/routes/helpers.ts

@@ -0,0 +1,62 @@
+import type { AuthUser } from "../auth/session"
+
+export function objectValue(value: unknown): Record<string, unknown> {
+  return value && typeof value === "object" && !Array.isArray(value)
+    ? (value as Record<string, unknown>)
+    : {}
+}
+
+export function stringArray(value: unknown): string[] {
+  return Array.isArray(value)
+    ? value.filter((item): item is string => typeof item === "string")
+    : []
+}
+
+export function queryInteger(
+  value: string | undefined,
+  fallback: number,
+  options: { min?: number; max?: number } = {},
+) {
+  const parsed = Number(value)
+  if (!Number.isInteger(parsed)) return fallback
+  if (options.min !== undefined && parsed < options.min) return fallback
+  if (options.max !== undefined && parsed > options.max) return fallback
+  return parsed
+}
+
+export function isRegularUser(user: AuthUser | null | undefined) {
+  return user?.adminType === "Regular User"
+}
+
+export function isAdminRole(user: AuthUser | null | undefined) {
+  return Boolean(user && user.adminType !== "Regular User")
+}
+
+export function isTeacherOrAbove(user: AuthUser | null | undefined) {
+  return user?.adminType === "Teacher Admin" || user?.adminType === "Super Admin"
+}
+
+export function isSuperAdmin(user: AuthUser | null | undefined) {
+  return user?.adminType === "Super Admin"
+}
+
+export function publicTemplates(value: unknown) {
+  const templates: Record<string, string> = {}
+  for (const [language, raw] of Object.entries(objectValue(value))) {
+    if (typeof raw !== "string") continue
+    const match = raw.match(/\/\/TEMPLATE BEGIN\n([\s\S]+?)\/\/TEMPLATE END/)
+    templates[language] = match?.[1] ?? ""
+  }
+  return templates
+}
+
+export function todayStart() {
+  const now = new Date()
+  now.setHours(0, 0, 0, 0)
+  return now.toISOString()
+}
+
+export function rounded(value: number, digits = 2) {
+  const factor = 10 ** digits
+  return Math.round(value * factor) / factor
+}