docs(directory): add @ssych registry

[savvasicevs]

Adds @ssych to the registry directory.

• Registry: https://ui.ssych.com/r/registry.json
• Homepage: https://ui.ssych.com
• Flat structure, files at the root (/r/{name}.json), no content property in files.
• Installs with the CLI as-is: npx shadcn@latest add @ssych/sidebar

Dark, data-dense components for high-stakes decision surfaces — trading books, screeners, clinical dashboards. Charts are hand-authored SVG with no chart runtime.

Replaces #11499, which accidentally re-encoded the non-ASCII characters in 31 unrelated entries. This one is a single 7-line addition on top of current main.

[vercel]

@savvasicevs 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.