fix(redis): 按事件循环隔离 Redis 连接，防止子线程 asyncio.run 导致连接泄漏

RedisClientManager 新增 _redis_by_loop 字典，按 event loop id 维护独立连接，
避免 usage consumer 在 asyncio.to_thread + asyncio.run 场景下复用主循环连接。

同步重构 consumer_streams 的写库路径：_apply_record_event 统一走
record_usage_batch，_apply_streaming_event 改为 to_thread 执行同步 DB 操作，
移除冗余的 session 传递和手动 rollback 逻辑。

tests/clients/test_redis_client.py

@@ -1,3 +1,7 @@
+import asyncio
+
+import pytest
+
 from src.clients import redis_client as redis_client_module
 from src.clients.redis_client import RedisClientManager, RedisState
 
@@ -39,3 +43,49 @@ def test_reset_redis_circuit_breaker_returns_false_when_uninitialized() -> None:
     finally:
         redis_client_module._redis_manager = old_global
         redis_client_module._usage_queue_redis_manager = old_usage
+
+
+@pytest.mark.asyncio
+async def test_get_redis_client_isolated_per_event_loop(monkeypatch: pytest.MonkeyPatch) -> None:
+    old_global = redis_client_module._redis_manager
+    try:
+        redis_client_module._redis_manager = RedisClientManager(client_name="global")
+
+        class DummyRedis:
+            def __init__(self, name: str) -> None:
+                self.name = name
+                self.closed = False
+
+            async def ping(self) -> bool:
+                return True
+
+            async def close(self) -> None:
+                self.closed = True
+
+        created_clients: list[DummyRedis] = []
+
+        async def fake_from_url(*args: object, **kwargs: object) -> DummyRedis:
+            client = DummyRedis(f"client-{len(created_clients)}")
+            created_clients.append(client)
+            return client
+
+        monkeypatch.setattr(redis_client_module.aioredis, "from_url", fake_from_url)
+
+        main_client = await redis_client_module.get_redis_client()
+
+        def _get_client_from_thread() -> object:
+            return asyncio.run(redis_client_module.get_redis_client())
+
+        thread_client = await asyncio.to_thread(_get_client_from_thread)
+
+        assert main_client is created_clients[0]
+        assert thread_client is created_clients[1]
+        assert thread_client is not main_client
+        assert redis_client_module.get_redis_client_sync() is main_client
+
+        await redis_client_module.close_redis_client()
+
+        assert created_clients[0].closed is True
+        assert created_clients[1].closed is True
+    finally:
+        redis_client_module._redis_manager = old_global