Fix missing Optional import in transaction_freeze.py

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

tasks/transaction_freeze.py

@@ -7,7 +7,7 @@ Runs on a schedule to increment weeks and process contested transactions.
 import asyncio
 import random
 from datetime import datetime, UTC
-from typing import Dict, List, Tuple, Set
+from typing import Dict, List, Tuple, Set, Optional
 from dataclasses import dataclass
 
 import discord