docs: add AI infrastructure procurement readiness

[afaryy]

Summary

• extend the CloudAI capability model with cloud and infrastructure foundations
• add applicability-led energy, grid, water, cooling, land-use, location, sustainability, and regulatory-readiness gates
• add one evidence-based AI supplier and procurement readiness contract
• distinguish current requirements, announced directions, planned standards, and watch items
• preserve public-safe non-claims for future legislation, supplier assurance, program participation, and data-centre deployment

Official signals

• National Cabinet communique, 26 August 2026
• National AI Centre Buy Australian AI Partnership Program

Validation

• API regression suite: 193/193 passed
• AgentCore runtime suite: 20/20 passed
• Argo CD GitOps contract checks passed
• changed-document relative links resolve
• git diff --check passed

Runtime boundary

Documentation and architecture-contract changes only. No AWS resource, GPU, EKS cluster, supplier service, application, or protected workflow was created or invoked.