Provide clarity on Cloud Run Terraform scope, add a pool audit and rollback checks

[harish-narayanappa-10]

Follow-up to the Cloud Run skill testing
https://github.com/temporalio/internal-ai-prototypes/blob/2026/10/temporal-serverless-skill-eval/analysis/analysis.pdf

The skill assumed one person deploying once. When asked to put pools in shared
Terraform, an agent kept state on one machine, and a new release could replace
or change an older build's pool.

• The Terraform module covers IAM only; pools are created with gcloud unless
  the user asks for Terraform.
• Short rules for Terraform-managed pools: one pinned pool per build, never
  updated; instance count left to Temporal; locked remote state.
• Pool audit: a checklist for reviewing an existing Worker Pool, marking
  anything it can't confirm as unverified.
• Rollback checks: confirm the previous version still exists before rolling
  back, and treat a missing or null Task Queue binding the same way.