Verify end-to-end Kamal deployment cycle on GCP

[justin808]

Context

Phase 1 dependency updates are merged (PRs #39-42). Before moving to Phase 2 (Control Plane), we need to verify the full deployment pipeline still works with all the updates.

Tasks

• Run terraform apply in terraform-gcloud/ to provision infrastructure
• Verify Cloud SQL, Compute Engine instance, firewall rules are correct
• Run kamal setup to deploy the app
• Verify app is live at https://gcp.kamaltutorial.com with SSL
• Test CRUD operations (Posts)
• Verify Solid Cache, Solid Queue, Solid Cable are working
• Verify Tailwind CSS v4 assets render correctly
• Run kamal app exec 'bin/rails db:seed' or similar smoke tests
• Document any issues encountered
• Tear down with terraform destroy to confirm clean teardown

Notes

This validates all the dependency updates work together in production. The DeploymentManager class in lib/ can automate most of this.

Related PRs

• Fix Dockerfile for psych gem and add ARM Mac build docs #47: Dockerfile fix for psych gem (must be merged first)
• Add deployment info footer showing git revision and build time #48: Deploy info footer (nice to have for verification)