Replace the previous mock/httptest-based conflict tests with
integration tests that exercise the full HTTP stack against a live
test server with a real database. Changes include:
- Add shared test helpers (setupConflictTest, createTestConflict,
makeConflictData) to reduce boilerplate across test files
- Split monolithic TestConflictDetection and TestConflictsBulkOperations
into focused test functions per scenario
- Test conflict detection, bulk resolution (most_recent, highest_progress,
manual strategies), and edge cases (empty IDs, invalid UUIDs,
unauthorized access)
- Verify actual database state after resolution, not just HTTP response