refactor: remove old architecture files deleted in b1832c9

Remove files that were deleted in b1832c9 (Stage 6 migration) but remained
on this branch due to merge conflicts:

- Remove .github/workflows/scripts/create-release-packages.{sh,ps1}
  (replaced by inline release.yml + uv tool install)
- Remove tests/test_core_pack_scaffold.py
  (scaffold system removed, tests no longer relevant)

These files existed on the feature branch because they were modified before
b1832c9 landed. The merge kept our versions, but they should be deleted to
align with the new integration-only architecture.

This PR now focuses purely on adding NEW Forge integration support, not
restoring old architecture.

Author: ericnoam