add e2e test suite for ucd-store-v2 #337
Description
The v2 store should have a comprehensive end-to-end test suite from the start, not just unit tests with mocked APIs and filesystems.
The e2e tests should use the actual UCD API and real temporary directories to verify that everything works together correctly in real-world scenarios. This would catch integration issues that mocks don't reveal, like URL construction bugs, file path issues across different operating systems, and edge cases in API responses.
Having these tests from the beginning ensures the store is production-ready and helps prevent regressions as we add new features.