architecture(roadmap): split IntegrationV2 stabilization into lifecycle, contracts, infra, and CI phases

The original IntegrationV2 stabilization phase was decomposed into
explicit architectural phases covering:

- Driver lifecycle & resolver responsibility
- IntegrationV2 contracts and decision locking
- Real infrastructure validation
- PHPUnit and CI governance

No tasks were removed or rewritten.
This change is structural only and preserves full historical intent.

Author: megyptm