fix: build cleanup and terminate on failure

[dwhswenson]

• Some failures were leaving behind AMIs (name prefaced by ami-builder-) that weren't getting cleaned up by the janitor. Added cleanup-related tags so the janitor would clean up failures.
• Some failures were shutting down by leaving the instance in a "stopped" state, with the EBS volume still active, meaning we were getting charged for EBS. This switches shutdown mode to "terminate," which will delete the EBS volume on failure (just as on success).

Assisted-by: Codex.app:GPT-5.6-Sol

[Copilot]

Pull request overview

This PR improves cleanup behavior for failed AMI builds by (1) ensuring failed-build artifacts are easier to identify/tag for automated cleanup and (2) changing the Packer instance shutdown behavior to terminate (to avoid leaving stopped instances/volumes behind on failure).

Changes:

• Add failed-build AMI detection (ami-builder- name tag prefix) and emit a warning when auto-delete cleans these up.
• Update Packer amazon-ebs config to shutdown_behavior = "terminate" and expand run_tags to include the merged cleanup tag set.
• Extend CLI tests to cover failed-build detection and the new auto-delete warning behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
cli/test_ami_cli.py	Adds test coverage for failed-build name-prefix detection and auto-delete warning/deletion behavior.
cli/ami_cli.py	Introduces failed-build AMI detection and warning output during auto-delete.
build-ami.pkr.hcl	Switches shutdown behavior to terminate and merges standard tags into run_tags to improve cleanup/traceability on failures.

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[ethanholz]

Looks good mergin.