CI: Add terraform test to PR workflow

## Description

CI currently runs TypeScript tests and Terraform validate, but does not execute `terraform test` for Terraform modules. This means `.tftest.hcl` tests aren’t enforced in PRs, allowing Terraform regressions to slip in.

## Proposal 

* Add a CI job to run `terraform test` for changed modules in a PR.
* Detect changed module directories and run: `terraform test`