Use timezone-aware build timestamp

backend/app/routers/system.py

@@ -1,7 +1,7 @@
 """System endpoints for core OS operations"""
 from fastapi import APIRouter, Depends
 from sqlalchemy.ext.asyncio import AsyncSession
-from datetime import datetime
+from datetime import UTC, datetime
 import os
 
 from app.config import settings
@@ -22,7 +22,7 @@ async def get_version():
 
     return {
         "version": settings.APP_VERSION,
-        "build_time": datetime.utcnow().isoformat(),
+        "build_time": datetime.now(UTC).isoformat(),
         "env": settings.ENVIRONMENT,
         "git_sha": git_sha[:8] if len(git_sha) > 8 else git_sha,
         "app_name": settings.APP_NAME,