Step 1 — Implementation Detail

Mapped the confirmed baseline to Cloud Run, Cloud SQL for PostgreSQL, Pub/Sub, Artifact Registry, Secret Manager, Cloud Logging, Cloud Monitoring, Cloud Trace, IAM, and Service Usage.
Documented request, persistence, event, retry/dead-letter, identity, and observability flows in architecture.md.
Added the architecture.mmd Mermaid flowchart and embedded an equivalent diagram in the guide.
Added Terraform for service enablement, Artifact Registry, Cloud SQL, Pub/Sub topics/subscription, Secret Manager placeholder, runtime service account, and Cloud Run API/worker services.
Parameterised project, region, name, images, SQL tier, HA, and deletion protection; supplied terraform.tfvars.example without secrets.