feat(skills): install remote orbit skill from the self-updating wrapper

Description

glab skills install orbit now installs a small wrapper skill. The wrapper loads the real Orbit skill from your installed glab orbit binary and GitLab instance, so you don't need to reinstall it to get updates. The skill is still called orbit everywhere you see it.

Related Issues

No public issue for this change.

How has this been tested?

• go test ./internal/commands/skills/... covers the name rewrite, a missing name, and the registry entry.
• make lint is clean.
• make gen-docs produced no changes.

Agent context

• The registry entry orbit now points at skills/orbit-wrapper (upstream frontmatter is name: orbit-wrapper).
• The fetcher rewrites the top-level frontmatter name of the fetched SKILL.md to the registry entry name, so the installed directory and frontmatter agree. Only the first name: line inside the frontmatter block changes; nested keys and the body are untouched. A SKILL.md without name fails the fetch.
• scripts/skills/add-remote gets --name to publish a skill under a different public name. Without it the old directory/name check still applies.
• The registry header comment documents the exception.
• Labels come from the repo MR template. No milestone set; the active ones listed are stale.
• Branch pipelines were not checked.