fix: center title-only toast content

[hruilabs]

A title-only toast such as “Saved” sits above its status icon and dismiss button. The row always uses top alignment: the title has a 20px line height, the controls are 28px high, and the icon has an additional 2px top margin.

Center the row and remove the icon offset when neither a description nor an action is present. Toasts with descriptions or actions keep their current top alignment. Add a persistent “Title only” preview, update the component date, and cover updating an existing toast from detailed content to a title only.

Reproduction

<AnimatedToastStack
  toasts={[{ id: "saved", title: "Saved", status: "success", duration: 0 }]}
  onDismiss={() => {}}
/>

Before this change, the icon center is 6px below the title center. All three elements should share a vertical center.

Validation

• bun run check passed: TypeScript, Biome lint, and all 82 registry components.
• bun test passed: 424 tests, including 6 toast regression cases. The title-only, empty-description, and details-removed cases failed before the fix.
• The local upstream preview was checked in Chromium: title, icon, and dismiss centers all measured at y=43px.
• The equivalent patch was also exercised in a consuming app with Chromium at 1280px and 390px: title/icon/dismiss centers align within 1px, description/action combinations retain top alignment, and dismissal, reduced motion, and short-viewport scrolling remain functional. Those browser checks use the consuming app's adapted component; the Bun tests here assert the upstream component's rendered layout classes because Happy DOM does not perform layout.

[starc007]

Thanks for fixing the toast alignment and adding the preview and regression coverage! Nice attention to detail.