Allow targeted package publishing

[Banegasn]

Summary

• Allow manual package releases to select one public package for npm and GitHub Packages.
• Reject unknown package names and document the scoped release command.
• Keep the existing all-package behavior when the selector is omitted.

Why

The rail 3.2.5 release succeeded in both registries, but the all-package GitHub Packages step also attempted 11 older versions and failed with permission_denied: write_package. A scoped run can complete cleanly without changing access to unrelated packages.

Verification

• bash -n scripts/publish-unpublished.sh and git diff --check
• Scoped npm and GitHub Packages checks skipped the already-published rail 3.2.5.
• An unknown package name exited with an error.