收紧后端 TypeScript：统一 Json 类型与 TaskContext 契约

关闭 allowJs；集中 JsonObject 定义并替换分散 any 别名；parseTaskContext 返回 TaskContext；任务详情 API 标注 AdminTaskDetailView；测试减少 as any。

apps/backend/src/services/admin/admin-auth-service.ts

@@ -1,4 +1,5 @@
 import crypto from 'node:crypto'
+import type { JsonObject } from '../../types/json.js'
 
 import { runtimeConfig } from '../../config/runtime.js'
 import {
@@ -15,8 +16,6 @@ import { normalizePage, normalizePageSize } from './admin-query-utils.js'
 
 type AdminUserRow = NonNullable<Awaited<ReturnType<typeof getAdminUserById>>>
 
-type JsonObject = Record<string, any>
-
 export type AdminSession = {
   sessionId: string
   userId: number