feat(排行榜): 页头显示当前在线人数，在线绿点只给老师

新增匿名可读的 GET /api/site/online，一条 ZCOUNT 让 Redis 自己数，
不拉成员、也不写（清理过期成员留给后台列表，匿名接口不带写操作）。
榜单页进页面拉一次，为 0 时不显示。

/rankings/users 的 isOnline 是三态：null 表示「这个调用方不该知道」，
只有老师及以上拿到 true/false。写成普通 boolean 的话学生看到的 false
和真的离线分不开，等于默认把每个人的在线状态摊给全校同学看。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xu912Rv5JUUuy6MqMcQW2

apps/api/src/routes/account.ts

@@ -33,6 +33,7 @@ import {
 import { Hono } from "hono"
 
 import { hashPassword } from "../auth/password"
+import { onlineUserIds } from "../auth/presence"
 import { optionalAuth, requireAuth, type AppEnv } from "../auth/middleware"
 import { config } from "../config"
 import { db, schema } from "../db"
@@ -40,7 +41,7 @@ import { failure, success } from "../http"
 import { JudgeStatus } from "../judge/status"
 import { getBooleanOption } from "../services/options"
 import { getUserProfileById } from "../services/profile"
-import { objectValue, queryInteger, sampleUser } from "./helpers"
+import { isTeacherOrAbove, objectValue, queryInteger, sampleUser } from "./helpers"
 
 export const accountRoutes = new Hono<AppEnv>()
 
@@ -184,7 +185,8 @@ accountRoutes.get("/rankings/users", optionalAuth, async (c) => {
   // 端点延迟从「四个来回相加」变成「最慢的那个」。越界页一条不剩，直接不发 SQL。
   const pageLimit = Math.max(0, Math.min(limit, LEADERBOARD_SIZE - offset))
 
-  const [totalRow, rows, me] = await Promise.all([
+  // 谁在线只给老师看，学生那边整列都是 null（见 rankProfileSchema.isOnline）
+  const [totalRow, rows, me, online] = await Promise.all([
     db.select({ value: count() }).from(schema.userProfile)
       .innerJoin(schema.user, eq(schema.userProfile.userId, schema.user.id))
       .where(leaderboardWhere).then(([row]) => row),
@@ -194,10 +196,11 @@ accountRoutes.get("/rankings/users", optionalAuth, async (c) => {
       .where(leaderboardWhere).orderBy(...leaderboardOrder)
       .limit(pageLimit).offset(offset),
     myLeaderboardRank(c.get("user")?.id),
+    isTeacherOrAbove(c.get("user")) ? onlineUserIds() : null,
   ])
 
   return success(c, userRankSchema.parse({
-    results: rows.map(serializeRankRow),
+    results: rows.map((row) => serializeRankRow(row, online)),
     total: Math.min(totalRow?.value ?? 0, LEADERBOARD_SIZE),
     me,
   }))
@@ -206,13 +209,14 @@ accountRoutes.get("/rankings/users", optionalAuth, async (c) => {
 function serializeRankRow({ profile, user }: {
   profile: typeof schema.userProfile.$inferSelect
   user: typeof schema.user.$inferSelect
-}) {
+}, online: Set<number> | null = null) {
   return rankProfileSchema.parse({
     id: profile.id,
     user: sampleUser(user, profile.realName),
     acceptedNumber: profile.acceptedNumber,
     submissionNumber: profile.submissionNumber,
     mood: profile.mood,
+    isOnline: online ? online.has(user.id) : null,
   })
 }
 

apps/api/src/routes/site.ts

@@ -1,8 +1,9 @@
-import { quoteSchema, websiteConfigSchema } from "@oj2/contract"
+import { onlineCountSchema, quoteSchema, websiteConfigSchema } from "@oj2/contract"
 import { asc, desc, eq } from "drizzle-orm"
 import { Hono } from "hono"
 import { resolve } from "node:path"
 
+import { onlineCount } from "../auth/presence"
 import { config } from "../config"
 import { db, schema } from "../db"
 import { failure, success } from "../http"
@@ -25,6 +26,14 @@ siteRoutes.get("/site", async (c) => {
   }))
 })
 
+/**
+ * 当前在线人数。匿名可读 —— 一个聚合数字不暴露任何人的身份，
+ * 而榜单页本身就允许匿名看。谁在线是另一回事，只在 /rankings/users 里对老师下发。
+ */
+siteRoutes.get("/site/online", async (c) => {
+  return success(c, onlineCountSchema.parse({ count: await onlineCount() }))
+})
+
 // 数据集读不到时的兜底（本机 dev 没挂 data/hitokoto 就会走这里）
 const fallbackQuotes = [
   { hitokoto: "程序首先是写给人读的，其次才是让机器执行。", from: "Structure and Interpretation of Computer Programs" },