Track infrastructure as code and cloud environments phase

[codeforester]

Track the infrastructure as code and cloud environments phase for Banyan Labs.

Intent:

• Model dev, staging, and production environments after local deployment and observability patterns are proven.
• Start with one cloud provider before expanding to a second.
• Add Terraform or OpenTofu modules for networking, Kubernetes, database, DNS, secrets, observability, and release environment wiring.
• Defer Crossplane or a similar control-plane pattern until the project has a clear need for it.

Completion direction:

• A non-production cloud environment can be provisioned, deployed, observed, and destroyed from documented automation.
• The environment model explains what differs between dev, staging, and production.
• Multi-cloud work is split into child issues only after one cloud path works end to end.
• Detailed child issues are created only when this phase is ready to execute.

Related roadmap issue: #32.