refactor(v2): isolate legacy provider stack and prune obsolete tests

tests/test_v2_runtime_boundaries.py

@@ -0,0 +1,15 @@
+import pytest
+from django.conf import settings
+
+
+@pytest.mark.django_db
+def test_legacy_provider_stack_disabled_by_default():
+    assert settings.LEGACY_PROVIDER_STACK_ENABLED is False
+    assert "apps.providers" not in settings.INSTALLED_APPS
+
+
+@pytest.mark.django_db
+def test_providers_route_not_mounted_by_default(client):
+    response = client.get("/providers/")
+    assert response.status_code == 404
+