#215 feat: mirror scaffold and update helper tests

 Add source-mirrored, dot-source-first Pester test files for the small
 and well-isolated helpers under src/private/scaffold and
 src/private/update so each unit-level helper has a focused test file
 under tests/private/scaffold or tests/private/update instead of being
 covered only through broad legacy coverage files. The remaining
 workflow-level scaffold and update helpers stay covered by the existing
 broad tests for now.

Author: stiwicourage