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>

packages/contract/src/achievement.ts

@@ -0,0 +1,51 @@
+import { z } from "zod"
+
+export const achievementRaritySchema = z.enum(["bronze", "silver", "gold", "platinum"])
+
+export const achievementSchema = z.object({
+  id: z.number().int(),
+  name: z.string(),
+  description: z.string(),
+  icon: z.string(),
+  rarity: achievementRaritySchema,
+  hidden: z.boolean(),
+  metric: z.string().nullable(),
+  operator: z.enum(["gte", "lte"]).nullable(),
+  threshold: z.number().int().nullable(),
+  unlocked: z.boolean(),
+  unlockTime: z.string().nullable(),
+  backfilled: z.boolean(),
+  progress: z.number().nullable(),
+  unlockRate: z.number(),
+})
+
+export const achievementListSchema = z.object({
+  username: z.string(),
+  achievements: z.array(achievementSchema),
+})
+
+export const pendingAchievementSchema = z.object({
+  id: z.number().int(),
+  name: z.string(),
+  description: z.string(),
+  icon: z.string(),
+  rarity: achievementRaritySchema,
+})
+
+export const achievementSummarySchema = z.object({
+  username: z.string(),
+  total: z.number().int(),
+  unlocked: z.number().int(),
+  percent: z.number(),
+  rarity: z.array(z.object({
+    rarity: achievementRaritySchema,
+    label: z.string(),
+    total: z.number().int(),
+    unlocked: z.number().int(),
+  })),
+  recent: z.array(pendingAchievementSchema),
+})
+
+export const markAchievementsReadSchema = z.object({
+  ids: z.array(z.number().int()),
+})