Streamline GitHub Actions pipeline and shift Lambda packaging to Terraform

[4Min4m]

Summary

• streamline the GitHub Actions workflow by collapsing builds into the Terraform plan/apply stages, introducing an A/B routing step, and enhancing the smoke tests
• move Lambda artifact packaging into Terraform-managed infrastructure and allow the LIVE alias to be adjusted outside of Terraform
• remove the legacy CodeBuild buildspec files and refresh the README to document the AWS/GitHub Actions deployment flow

Testing

• not run (infrastructure definition updates only)

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Codex Task