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/events.ts

@@ -0,0 +1,48 @@
+import { flowchartUpdateSchema, type FlowchartUpdate } from "@oj2/contract"
+
+import { redis } from "./redis"
+
+export const userEventChannel = "user:events"
+
+interface UserEvent {
+  userId: number
+  data: FlowchartUpdate | Record<string, unknown>
+}
+
+interface AchievementNotification {
+  id: number
+  name: string
+  description: string
+  icon: string
+  rarity: string
+  kind: "achievement" | "badge"
+}
+
+export function userEventTopic(userId: number) {
+  return `events:user:${userId}`
+}
+
+export async function publishFlowchartUpdate(userId: number, data: FlowchartUpdate) {
+  await redis.publish(userEventChannel, JSON.stringify({ userId, data: flowchartUpdateSchema.parse(data) }))
+}
+
+export async function publishAchievementNotification(
+  userId: number,
+  achievements: AchievementNotification[],
+) {
+  if (!achievements.length) return
+  await redis.publish(userEventChannel, JSON.stringify({
+    userId,
+    data: { type: "achievement_unlocked", achievements },
+  }))
+}
+
+export function parseUserEvent(raw: string): UserEvent | null {
+  try {
+    const value = JSON.parse(raw) as UserEvent
+    if (!Number.isInteger(value.userId) || !value.data || typeof value.data !== "object") return null
+    return value
+  } catch {
+    return null
+  }
+}