Fix missing Request import in observability router

- Add missing Request import to backend/routers/observability.py
- This was causing 'name Request is not defined' error on startup

backend/routers/observability.py

@@ -20,7 +20,7 @@ from typing import Dict, List, Optional, cast
 import psutil
 from utils.environment import get_environment_info, debug_environment
 import requests
-from fastapi import APIRouter, Depends, HTTPException
+from fastapi import APIRouter, Depends, HTTPException, Request
 from fastapi.responses import JSONResponse
 from langsmith import Client as LangsmithClient
 from pydantic import BaseModel