* fix(cutover): write Slack secrets into empty Terraform shells
DescribeSecret succeeds on HCP-created shells with no version, so skip-if-exists left roster and Slack tokens unset.
* feat(infra): migrate afterhours to HCP Terraform (PLAT-74)
Replace the mgmt SAM stack with a prod-only HCP workspace, in-repo hcptf IAM, stub Lambdas, and zip CD on push to main.
* fix(cutover): retry DDB unprocessed items and skip past at() holidays
Unprocessed BatchWriteItem rows and leftover past at() schedules would drop roster data or abort holiday recreation during prod cutover.
