refactor(api): 请求体解析收成 readJson / parseBody

54 处 handler 都手写同一段：
  const parsed = X.safeParse(await c.req.json().catch(() => null))
  if (!parsed.success) return failure(c, 400, "invalid-request", ...)
漏写 .catch 就是一个畸形请求打出 500。

- http.ts 加 readJson（读 + 校验）和 parseBody（再加上 400）。parseBody 不给
  message 时回 zod 的第一条 issue —— 后台表单原来就是这么写的，fallback 文案
  「Invalid payload」/「参数错误」只在 issues 为空时才用得上，实际走不到
- 51 处换成 parseBody；另 3 处失败时带别的错误码或和路径参数一起判，换成 readJson
- 错误码、状态码、文案、判断顺序都不变

实跑核过：非 JSON 请求体回原来的固定文案，公告标题为空回 zod issue。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/api/src/routes/admin/contest.ts

@@ -12,7 +12,7 @@ import { Hono } from "hono"
 import { requireTeacher, type AppEnv } from "../../auth/middleware"
 import type { AuthUser } from "../../auth/session"
 import { db, schema } from "../../db"
-import { failure, success } from "../../http"
+import { failure, parseBody, success } from "../../http"
 import { contestStatus } from "../../services/contest"
 import { objectValue, queryInteger, sampleUser } from "../helpers"
 
@@ -120,17 +120,8 @@ adminContestRoutes.get("/contests/:id", requireTeacher, async (c) => {
 })
 
 adminContestRoutes.post("/contests", requireTeacher, async (c) => {
-  const parsed = createContestRequestSchema.safeParse(
-    await c.req.json().catch(() => null),
-  )
-  if (!parsed.success) {
-    return failure(
-      c,
-      400,
-      "invalid-request",
-      parsed.error.issues[0]?.message ?? "Invalid payload",
-    )
-  }
+  const parsed = await parseBody(c, createContestRequestSchema)
+  if (!parsed.success) return parsed.response
   const error = validatePayload(parsed.data)
   if (error) return failure(c, 400, "invalid-contest", error)
 
@@ -157,17 +148,8 @@ adminContestRoutes.post("/contests", requireTeacher, async (c) => {
 
 adminContestRoutes.put("/contests/:id", requireTeacher, async (c) => {
   const id = queryInteger(c.req.param("id"), 0, { min: 1 })
-  const parsed = updateContestRequestSchema.safeParse(
-    await c.req.json().catch(() => null),
-  )
-  if (!parsed.success) {
-    return failure(
-      c,
-      400,
-      "invalid-request",
-      parsed.error.issues[0]?.message ?? "Invalid payload",
-    )
-  }
+  const parsed = await parseBody(c, updateContestRequestSchema)
+  if (!parsed.success) return parsed.response
   const [existing] = await selectContest(id)
   if (!existing || !ownedBy(c.get("user")!, existing.contest)) {
     return failure(c, 404, "contest-not-found", "Contest does not exist")
@@ -386,17 +368,8 @@ adminContestRoutes.put(
   requireTeacher,
   async (c) => {
     const contestId = queryInteger(c.req.param("id"), 0, { min: 1 })
-    const parsed = updateAcmHelperRequestSchema.safeParse(
-      await c.req.json().catch(() => null),
-    )
-    if (!parsed.success) {
-      return failure(
-        c,
-        400,
-        "invalid-request",
-        parsed.error.issues[0]?.message ?? "Invalid payload",
-      )
-    }
+    const parsed = await parseBody(c, updateAcmHelperRequestSchema)
+    if (!parsed.success) return parsed.response
     const [contest] = await db
       .select()
       .from(schema.contest)