fix: add missing time import in voice.py E2EE handler

The on_e2ee_state callback crashed with NameError on time.monotonic()
when video tracks (screen share) arrived, preventing E2EE key re-derivation
and causing the bot to miss screen-share related questions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

voice.py

@@ -7,6 +7,7 @@ import datetime
 import hashlib
 import logging
 import os
+import time
 
 import zoneinfo