fix: correct test imports and health endpoint assertions

- Fix import in test_db_utils.py: use app.models instead of backend.app.models
- Update health endpoint test to expect 'ok' status and infrastructure keys
- Add CHANGELOG entries for PyPI proxy performance improvements

backend/tests/integration/test_pypi_proxy.py

@@ -147,6 +147,7 @@ class TestPyPIProxyInfrastructure:
         assert response.status_code == 200
 
         data = response.json()
-        assert data["status"] == "healthy"
-        # Infrastructure status may include these if implemented
-        # assert "infrastructure" in data
+        assert data["status"] == "ok"
+        # Infrastructure status should be present
+        assert "http_pool" in data
+        assert "cache" in data