fix: suppress mypy no-untyped-call for redis.asyncio.from_url

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

backend/app/core/rate_limit.py

@@ -32,7 +32,7 @@ def _get_async_redis(redis_url: str) -> aioredis.Redis:
     """Return a shared async Redis client for *redis_url*, creating one if needed."""
     client = _async_redis_clients.get(redis_url)
     if client is None:
-        client = aioredis.from_url(redis_url)
+        client = aioredis.from_url(redis_url)  # type: ignore[no-untyped-call]
         _async_redis_clients[redis_url] = client
     return client