Function enhanceToast

Adopt (or create) a polite live region and expose an imperative API for showing and dismissing toasts. Declarative [data-hl-toast-trigger] buttons are handled through event delegation, so triggers added later need no re-enhancement. Hovering or focusing a toast pauses its auto-dismiss timer, danger toasts are announced assertively, and every show/dismiss is observable through onOpenChange/hl:open-change. Outside a browser this is a safe no-op that returns an empty handle. Markup can set data-hl-duration on the region.