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/problem.ts

@@ -28,7 +28,7 @@ import { optionalAuth, type AppEnv } from "../auth/middleware"
 import { db, schema } from "../db"
 import { failure, success } from "../http"
 import { JudgeStatus } from "../judge/status"
-import { objectValue as toObject, queryInteger } from "./helpers"
+import { objectValue as toObject, queryInteger, sampleUser } from "./helpers"
 
 export const problemRoutes = new Hono<AppEnv>()
 
@@ -83,7 +83,7 @@ function listItem(
 		submissionNumber: row.problem.submissionNumber,
 		acceptedNumber: row.problem.acceptedNumber,
 		difficulty: row.problem.difficulty,
-		createdBy: { id: row.user.id, username: row.user.username, realName: row.realName },
+		createdBy: sampleUser(row.user, row.realName),
 		tags: tags.get(row.problem.id) ?? [],
 		contestId: row.problem.contestId,
 		allowFlowchart: row.problem.allowFlowchart,
@@ -327,11 +327,7 @@ problemRoutes.get("/problems/:displayId", optionalAuth, async (c) => {
 		shareSubmission: row.problem.shareSubmission,
 		contestId: row.problem.contestId,
 		tags: tagRows.map((tag) => tag.name),
-		createdBy: {
-			id: row.creatorId,
-			username: row.creatorUsername,
-			realName: null,
-		},
+		createdBy: sampleUser({ id: row.creatorId, username: row.creatorUsername }, null),
 		myStatus,
 		myFailedCount,
 		allowFlowchart: row.problem.allowFlowchart,