feat: make patchright optional, default to stock playwright

tests/conftest.py

@@ -0,0 +1,11 @@
+"""Shared test fixtures."""
+
+import os
+
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def _clean_backend_env(monkeypatch):
+    """Ensure CLOAKBROWSER_BACKEND doesn't leak into tests from the host environment."""
+    monkeypatch.delenv("CLOAKBROWSER_BACKEND", raising=False)