FEAT-013 T021: un-skip US1 integration acceptance test (test_story1)

[brettheap]

Reopened by `/speckit.analyze` — T021 was prematurely marked `[x]` while its test is `pytest.mark.skip`-gated, so the US1 (P1 MVP) acceptance scenarios never execute end-to-end. Only contract-level tests (T016–T020, fake backends) run today.

What's needed

Remove the module-level `pytest.mark.skip` from `tests/integration/test_story1_create_standard_layout.py` and confirm US1 acceptance scenarios 1–3 pass against a real bench container.

Blocked by

• FEAT-013 T057b: US1 end-to-end — real integration bodies + launch-exit detection #30 (T057b) — authoring the real integration-test bodies + a live bench-container harness is the prerequisite. T057 (commit 52f41c1) already delivered the production tmux spawn backend this test depends on.

Tracked in `specs/013-managed-session-lifecycle/tasks.md` as T021.