v4.0.0-rc3

• Switched AWS authentication to SSO-only flow using aws login --remote, replacing aws configure.
• Exported SSO credentials to AWS config so Terraform and Packer can use them.
• Optimized Dockerfile cache by copying only Packer files instead of entire repo early in build.

Full Changelog: v4.0.0-rc2...v4.0.0-rc3