Refactors the Cloud Build pipelines to a modular and branch-aware setup, resolving redundancy and adding core features.
- `cloudbuild.opax-mcp.yaml`: A new, single pipeline for the OPAX-MCP service. It supports building from any branch, tags images with both branch name and commit SHA, and includes a placeholder for Tyr policy validation. Deployment to Cloud Run is conditional, running only for `main` and `opax-*` branches.
- `cloudbuild.base.yaml`: A new architecture file that explains the CI/CD structure. It clarifies that `cloudbuild.opax-mcp.yaml` is the single source of truth.
- `cloudbuild.yaml`, `cloudbuild.mcp.yaml`: These files are now deprecated. Their contents have been replaced with a notice pointing to the new pipeline to avoid confusion.
