Automate repeatable EC2 CodeDeploy releases

[ali509]

Summary

• add a manually triggered GitHub Actions workflow for immutable EC2 CodeDeploy releases
• deploy backend before frontend and restore bootstrap alarm settings even on failure
• derive the Secrets Manager region from the secret ARN when AWS_REGION is unavailable
• document ECS and EC2 deployment and verification steps

Validation

• 7 backend tests passed
• frontend lint and production build passed
• Docker Compose configuration validated
• frontend and backend CodeDeploy ZIP integrity checks passed
• workflow YAML parsed successfully