fix(阶段3): 匿名不可读用户档案，真名改为默认不下发

F1：GET /profiles/:username 只挂了 optionalAuth、handler 内无登录判断，
匿名可读 email、adminType、className、lastLogin。用户名又能经 /rankings/users
公开枚举，等于可以无 cookie 批量收集全校学生的邮箱与最后登录时间。
handler 开头补上未登录即返回空，对齐旧后端 account/views/oj.py 的
UserProfileAPI.get 首行 `if not user.is_authenticated: return self.success()`。

F2：旧后端把「是否下发真名」做成 UsernameSerializer(need_real_name=False)
的默认关闭开关，全仓 11 处调用只有比赛榜单一处显式打开；新后端没搬这一层，
真名随用户对象无条件下发，13 个下发点里 8 个匿名可达。

这里补回同一层：helpers.ts 新增 sampleUser()，realName 默认不下发，
需要的地方显式传 { includeRealName: true }。12 个下发点改为走这个函数，
只有比赛榜单一处打开（对齐 contest/serializers.py:84 的 is_contest_admin）。
没有逐处删字段 —— 那样下次新增端点还会重犯。

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

apps/api/src/routes/problemset.ts

@@ -33,7 +33,7 @@ import { publishAchievementNotification } from "../events"
 import { failure, success } from "../http"
 import { JudgeStatus } from "../judge/status"
 import { updateAchievementsForProblemSet } from "../services/achievements"
-import { isTeacherOrAbove, objectValue, queryInteger } from "./helpers"
+import { isTeacherOrAbove, objectValue, queryInteger, sampleUser } from "./helpers"
 
 export const problemsetRoutes = new Hono<AppEnv>()
 
@@ -59,7 +59,7 @@ async function problemSetCreator(id: number) {
   const [row] = await db.select({ id: schema.user.id, username: schema.user.username, realName: schema.userProfile.realName })
     .from(schema.user).leftJoin(schema.userProfile, eq(schema.userProfile.userId, schema.user.id))
     .where(eq(schema.user.id, id)).limit(1)
-  return row ?? { id, username: "", realName: null }
+  return sampleUser(row ?? { id, username: "" }, row?.realName)
 }
 
 function badgeData(badge: typeof schema.problemsetBadge.$inferSelect, earned?: boolean) {
@@ -166,7 +166,7 @@ problemsetRoutes.get("/problem-sets/:id/problems", optionalAuth, async (c) => {
       submissionNumber: problem.submissionNumber,
       acceptedNumber: problem.acceptedNumber,
       difficulty: problem.difficulty,
-      createdBy: { id: user.id, username: user.username, realName },
+      createdBy: sampleUser(user, realName),
       tags: tags.get(problem.id) ?? [],
       contestId: problem.contestId,
       allowFlowchart: problem.allowFlowchart,
@@ -395,7 +395,7 @@ problemsetRoutes.get("/problem-sets/:id/user-progress", requireAuth, async (c) =
   const results = rows.map(({ progress, user: progressUser, realName }) => problemSetProgressSchema.parse({
     id: progress.id,
     problemsetId: progress.problemsetId,
-    user: { id: progressUser.id, username: progressUser.username, realName },
+    user: sampleUser(progressUser, realName),
     joinTime: progress.joinTime,
     completeTime: progress.completeTime,
     isCompleted: progress.isCompleted,