feat(board): Lightning-paid message board with LNbits and admin moderation

Add public /board flow: create invoice, webhook + confirm reconciliation, list
active messages, likes (Nostr), zap fallbacks. Admin table for hide/delete.

Include LNbits webhook body normalization (double-encoded JSON), POST
/api/messages/confirm/:hash, and root npm db:push script. Prisma models for
pending invoices and board messages.

Made-with: Cursor

frontend/app/board/layout.tsx

@@ -0,0 +1,16 @@
+import type { Metadata } from "next";
+
+export const metadata: Metadata = {
+  title: "Message Board — Pay with Lightning",
+  description:
+    "Post a public message on the Belgian Bitcoin Embassy board. Pay a small Lightning invoice via LNbits to publish.",
+  openGraph: {
+    title: "Message Board — Belgian Bitcoin Embassy",
+    description: "Pay with Lightning to post a message.",
+  },
+  alternates: { canonical: "/board" },
+};
+
+export default function BoardLayout({ children }: { children: React.ReactNode }) {
+  return children;
+}