feat(teacher-bff): 添加视口聚合端点 + 修复身份头读取

- 新增 GET /teacher/viewports 聚合 IAM 视口配置
- 修复 controller 从 x-user-id header 读取身份（替代 AuthenticatedRequest）
- 添加 zod + @types/express 依赖

services/teacher-bff/package.json

@@ -19,10 +19,12 @@
     "prom-client": "^15.1.0",
     "@opentelemetry/api": "^1.9.0",
     "reflect-metadata": "^0.2.2",
-    "rxjs": "^7.8.0"
+    "rxjs": "^7.8.0",
+    "zod": "^3.23.0"
   },
   "devDependencies": {
     "@nestjs/cli": "^10.4.0",
+    "@types/express": "^4.17.0",
     "@types/node": "^22.0.0",
     "eslint": "^9.10.0",
     "typescript": "^5.6.0",