fix(trail): repair test build after auth-fallback demolition

trail_cmd_test.go referenced auth test helpers (newAuthMemStore, newResolveTestManager, auth.SetManagerForTest, auth.DiscoveryUnavailableForTest) that were deleted in #1410 (COR-393, "demolish auth fallbacks", commit 10aa97eec). The trail PR that added these tests (#... merged separately) and the demolition PR were both green in isolation, so the semantic conflict only surfaced on main once both had merged — mise run lint fails with typecheck errors.

Rewrite the two affected tests to use the surviving discovery seam (auth.SetResolveContextForAPIForTest) plus tokenstore.UseFileBackendForTesting, mirroring the working pattern already used by activity_cmd_test.go. Behaviour asserted is unchanged: not-logged-in still surfaces ErrNotLoggedIn + the login hint, and option validation still short-circuits before any auth resolution.