feat: add minimum viable terraform stack for hosted gcp

[sammargolis]

Summary

• adds Terraform modules for Cloud Run, Firestore, Redis, Secret Manager, and Artifact Registry
• adds dev/staging/prod environment roots and examples
• adds Terraform plan/apply workflows for reviewable infra changes

Security impact

• enables infra-as-code review path for hosted deployment controls
• supports least-privilege and secret management patterns through dedicated resources

PHI handling impact

• infra scaffolding only; no application PHI data path changes
• establishes deployable hosted baseline for compliant runtime controls

Tests executed

• pnpm build:test
• Terraform workflow validates/plans in CI (terraform init/validate/plan path)

Rollback plan

• revert this PR to remove Terraform hosted stack scaffolding