Feature Request: Add an Empty component

[suxiaoshao]

Description

Add a composable Empty component for empty results, missing content, first-use states, and other no-data presentations.

The component should follow the current shadcn/ui composition model instead of requiring each application to rebuild the same centered icon, title, description, and action layout.

Proposed parts

• Empty
• EmptyHeader
• EmptyMedia with default and icon variants
• EmptyTitle
• EmptyDescription
• EmptyContent

Actions and custom content should remain composable children.

Previous work

PR #2314 attempted an Empty component. It was closed without merging after a request to follow the shadcn style and later became inactive. Its implementation and screenshot may still be useful reference material.

Reference

• shadcn/ui Empty source

Acceptance criteria

• Stateless, composable component parts following existing GPUI builder patterns
• Theme-token-based styling with no component-specific global theme fields
• Story covering minimal, icon, action, search-result, and constrained-container examples
• English documentation in website/docs/components/
• Chinese documentation in website/zh-CN/docs/components/
• Builder-pattern test