TiDB Labs design-system reference for LLMs

Scope
- This repo does not publish a separate design system package. The source of
  truth is the existing frontend code in `frontend/`.

Working assumptions
- Preserve established component patterns unless the task is explicitly a
  redesign.
- Favor repo-local primitives and styles over introducing a new UI framework.
- Treat copy, localization, and API-mode behavior as part of the product
  contract, not as cosmetic details.

Useful anchors
- `frontend/src/app/**`
- `frontend/src/components/**`
- `frontend/src/app/globals.css`
- `frontend/package.json`