feat(infra): PR #5 — Terraform network + ECR foundation

[devin-ai-integration]

Summary

Wave 2 / PR #5. First IaC PR: a self-contained Terraform root infra/network/ for the VPC/networking foundation + the ECR registry. Small and app-agnostic; later IaC PRs (#6 storage, #7 compute, #8 M2+scheduler) consume its outputs. Establishes the shared naming/tag convention and the infra/ layout via infra/README.md.

infra/
  README.md            # per-domain layout + shared convention (name_prefix, tags)
  .gitignore           # terraform state/.terraform/lockfile
  network/
    versions.tf        # TF >=1.5, aws ~>5.0; no backend committed (validates offline)
    variables.tf       # project, environment(dev/test/prod), aws_region, vpc_cidr, az_count, programs
    main.tf            # VPC, public/private subnets x AZ, IGW, 1x NAT, routes, batch SG (8080 in-VPC)
    ecr.tf             # aws_ecr_repository per var.programs (scan_on_push + lifecycle keep-last-10)
    outputs.tf         # vpc_id, subnet ids, batch_security_group_id, ecr_repository_urls

Parameterized so services onboard by config: var.programs = ["cbtrn02c"] drives ECR repos via for_each; var.environment feeds the name_prefix. Dataset naming untouched (AWS.M2.CARDDEMO.*).

Verified locally

• terraform fmt -check, terraform init -backend=false, terraform validate → Success! The configuration is valid.

Links

• docs/modernization/CURRENT_STATE_ANALYSIS.md §6, §8
• Consumers: PR Add alphanumeric validation for User ID - MBA-123 #7 (compute) and Implement automated test suite for CICS login transaction CC00 (MBA-215) #8 (M2) use vpc_id/subnet/SG/ECR outputs.

Link to Devin session: https://app.devin.ai/sessions/c0f261ce337a4aee965332f1754d037a
Requested by: @vibhaseshadri-cognition

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