Add full SEO optimization for Spanglish social and language events

- Add comprehensive metadata to root layout with Open Graph, Twitter cards
- Create dynamic sitemap.ts for all pages and events
- Create robots.ts with proper allow/disallow rules
- Add JSON-LD Event structured data to event detail pages
- Add page-specific metadata to events, community, contact, FAQ pages
- Add FAQ structured data schema
- Update footer with local SEO text for Asunción, Paraguay
- Add web manifest for mobile SEO
- Create 404 page with proper noindex
- Optimize image alt text and add lazy loading
- Add NEXT_PUBLIC_SITE_URL env variable
- Add about/ folder to gitignore

frontend/src/app/not-found.tsx

@@ -0,0 +1,41 @@
+import type { Metadata } from 'next';
+import Link from 'next/link';
+
+export const metadata: Metadata = {
+  title: 'Page Not Found – Spanglish',
+  description: 'The page you are looking for could not be found.',
+  robots: {
+    index: false,
+    follow: true,
+  },
+};
+
+export default function NotFound() {
+  return (
+    <div className="min-h-screen flex items-center justify-center bg-secondary-gray">
+      <div className="text-center px-4">
+        <h1 className="text-6xl font-bold text-primary-dark mb-4">404</h1>
+        <h2 className="text-2xl font-semibold text-gray-700 mb-4">
+          Page Not Found
+        </h2>
+        <p className="text-gray-600 mb-8 max-w-md mx-auto">
+          The page you are looking for might have been removed, had its name changed, or is temporarily unavailable.
+        </p>
+        <div className="flex flex-col sm:flex-row gap-4 justify-center">
+          <Link
+            href="/"
+            className="inline-flex items-center justify-center px-6 py-3 bg-primary-yellow text-primary-dark font-semibold rounded-btn hover:bg-primary-yellow/90 transition-colors"
+          >
+            Go Home
+          </Link>
+          <Link
+            href="/events"
+            className="inline-flex items-center justify-center px-6 py-3 border-2 border-primary-dark text-primary-dark font-semibold rounded-btn hover:bg-primary-dark hover:text-white transition-colors"
+          >
+            View Events
+          </Link>
+        </div>
+      </div>
+    </div>
+  );
+}