/setup --prefix bug

[timezyme]

The problem: ./setup --prefix correctly creates symlinks (gstack-qa → gstack/qa),
but the name: field inside each SKILL.md isn't updated to match. Claude Code
uses the name: frontmatter field for skill registration, not the directory name.

• gstack-upgrade works because its SKILL.md says name: gstack-upgrade
• gstack-qa doesn't work because its SKILL.md still says name: qa
• Same for all other skills — the SKILL.md name: field was never patched