refactor: replace datetime.utcnow() with timezone-aware datetime.now(UTC)

server/environment.py

@@ -1,7 +1,7 @@
 import uuid
 import logging
 from typing import Optional, Callable
-from datetime import datetime
+from datetime import datetime, timezone
 
 from models import (
     AttackAction,
@@ -37,7 +37,7 @@ class RedTeamEnvironment:
         self.attack_history = []
         self.episode_id     = f"ep_{uuid.uuid4().hex[:12]}"
         self.is_active      = True
-        self.created_at     = datetime.utcnow()
+        self.created_at     = datetime.now(timezone.utc)
 
         if self.reward_computer and hasattr(self.reward_computer, "reset"):
             self.reward_computer.reset()