Native cmdlet equivalent of install.sh: same behavior (copy each
skills/<name>/ into ~\.claude\skills\<name>\, skip if SKILL.md is
missing, support $env:CLAUDE_SKILLS_DIR override and -Names filter).
Removes bash dependency on Windows — no need to invoke git-bash from
pwsh, mirrors the existing build.sh / build.ps1 pair.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
