feat: add SEO metadata, llms.txt, and markdown page mirrors

Centralize site metadata and social URLs for JSON-LD, expose llmstxt.org
content and per-page .md routes for LLM crawlers, and refactor blog/FAQ/events
pages with shared components.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/board/layout.tsx

@@ -1,4 +1,5 @@
 import type { Metadata } from "next";
+import { BreadcrumbJsonLd } from "@/components/public/JsonLd";
 
 export const metadata: Metadata = {
   title: "Message Board — Pay with Lightning",
@@ -12,5 +13,15 @@ export const metadata: Metadata = {
 };
 
 export default function BoardLayout({ children }: { children: React.ReactNode }) {
-  return children;
+  return (
+    <>
+      <BreadcrumbJsonLd
+        items={[
+          { name: "Home", href: "/" },
+          { name: "Board", href: "/board" },
+        ]}
+      />
+      {children}
+    </>
+  );
 }