Add initial plugin implementation and development setup

dev/app/layout.tsx

@@ -0,0 +1,14 @@
+import type { Metadata } from 'next'
+
+export const metadata: Metadata = {
+  title: 'Payload Notifications Plugin Demo',
+  description: 'Demo environment for the @xtr-dev/payload-notifications plugin',
+}
+
+export default function RootLayout({
+  children,
+}: {
+  children: React.ReactNode
+}) {
+  return children
+}