feat: introduce core-events package with event bus, hooks, and a web showcase demo

packages/core-events/src/index.ts

@@ -0,0 +1,14 @@
+// ─── Event Registry ─────────────────────────────────────────────
+export type {
+  AppEvents,
+  PrintReceiptPayload,
+  StockUpdatePayload,
+  ProfileUpdatedPayload,
+  ReceiptItem,
+} from './events.registry';
+
+// ─── Event Bus (Core) ───────────────────────────────────────────
+export { eventBus, publish, subscribe } from './event-bus';
+
+// ─── React Hooks ────────────────────────────────────────────────
+export { useAppEvent, usePublishEvent } from './hooks';