Fix: add future annotations to all files, fix date field name shadowing type in RewardRedeemRequest

backend/app/database.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
 from sqlalchemy.orm import DeclarativeBase
 from app.config import get_settings