feat(registry): add @livedocs to the registry directory

[berlified]

Summary

Adds the livedocs registry (https://livedocs.xyz) to apps/v4/registry/directory.json as @livedocs.

• Item URL pattern: https://livedocs.xyz/r/{name}.json
• Registry index: https://livedocs.xyz/r/registry.json (flat; files carry no content)
• Open source (MIT): https://github.com/berlified/livedocsxyz
• Charts (area, line, bar, pie, radar, radial, sankey, KPI/metric cards, meters) and UI primitives (button, card, badge, input, avatar, separator) built on semantic shadcn tokens.

Validation:

• pnpm validate:registries passes
• npx shadcn@latest registry validate on the source registry passes (29 items)
• Installed end-to-end in a fresh project via npx shadcn@latest add @livedocs/trend-card after registry add @livedocs=https://livedocs.xyz/r/{name}.json

[vercel]

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[github-actions]

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

[shadcn]

Thanks for the contribution. This entry is included in #11861. Closing this PR in favor of the combined update.