接入 ESLint 并清理未使用代码

- 前后端接入 ESLint 10 扁平配置（typescript-eslint 类型感知检查 + react-hooks/react-refresh），新增 lint / lint:check / lint:fix 脚本并纳入 check 链路
- 清理全部 no-unused-vars 与 no-useless-assignment 警告，修复 floating promises、正则转义等问题
- 删除确认无引用的死代码（markKuaishouCloudBindUrlRefreshFailed、未使用 helper 等）

apps/backend/src/services/admin/admin-read-shared-helpers.ts

@@ -1,6 +1,6 @@
 import { safeParseJson } from './admin-query-utils.js'
 import { normalizeAdminRole } from './admin-auth-service.js'
-import { asJsonObject, type JsonObject, JsonRecord } from '../../types/json.js'
+import { asJsonObject, type JsonRecord } from '../../types/json.js'
 import {
   parseTaskContext as parseTaskContextValue,
   parseTaskState as parseTaskStateValue,
@@ -379,7 +379,7 @@ export function createAdminViewerContext(
 
 export async function resolveAdminTaskScreenshotUrl(
   task: TaskLike,
-  viewerContext: AdminViewerContext,
+  _viewerContext: AdminViewerContext,
 ): Promise<string> {
   if (task.screenshot_path || task.runtime_session_id) {
     return `/api/v1/admin/tasks/${task.id}/screenshot`