test(auth): force in-memory backend for wx-qr session unit tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_wx_qr_session.py

@@ -1,10 +1,15 @@
 """wx_qr_session 状态机与一次性消费。"""
 import time
 
+import pytest
+
 from app.services import wx_qr_session as s
 
 
-def setup_function():
+@pytest.fixture(autouse=True)
+def force_memory_backend(monkeypatch):
+    """本地 .env 常有 REDIS_HOST；单测强制走进程内存，避免连真实 Redis。"""
+    monkeypatch.setattr(s, "_redis", lambda: None)
     s._memory_clear_for_tests()