Step 16 of v4.1 — first test in tests/integration/, establishes the
skip-on-missing-tool pattern voyage will reuse for environment-dependent
integration tests. Two tests:
1. compose config parses and contains expected services
2. compose config pins required image versions
Both skip cleanly when 'docker info' fails (no Docker installed). On a
machine with Docker, both tests run docker compose config and assert the
4 services + 3 version pins are present.
Tests: 468 pass + 2 skipped (Docker not installed in dev env).
