feat(registry): add @selectcodes to the directory

[Junhan2]

Adds @SelectCodes (https://select.codes) to the registry directory.

• Registry index: https://select.codes/r/registry.json — name, homepage, 173 items
• Item URL template: https://select.codes/r/{name}.json (e.g. glimmer-skeleton)
• Verified end to end: npx shadcn@latest add https://select.codes/r/glimmer-skeleton.json installs into components/ui in a fresh project; free items are public, gated items answer 401 with a setup guide
• Agent surfaces available: /llms.txt, /llms-full.txt, and per-component .md twins

One entry added at its sorted position; the rest of the file is byte-identical.

[vercel]

@Junhan2 is attempting to deploy a commit to the shadcn-pro Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

Can you sign the commits please? See https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits. Thank you.