feat: add Spinner, EmptyState, StatCard (v0.4.0)

Harvested from delta. StatCard integrates AnimatedNumber + intent colors;
EmptyState and Spinner generalize delta's local versions for reuse.

src/index.ts

@@ -21,6 +21,9 @@ export {
 } from "./components/dropdown-menu";
 export { Table, TableHeader, TableBody, TableRow, TableHead, TableCell } from "./components/table";
 export { Toaster, toast } from "./components/toast";
+export { Spinner, type SpinnerProps } from "./components/spinner";
+export { EmptyState, type EmptyStateProps } from "./components/empty-state";
+export { StatCard, type StatCardProps, type StatIntent } from "./components/stat-card";
 
 // Motion
 export { FadeIn, Stagger, StaggerItem, staggerContainer, staggerItem, motion } from "./motion";