feat: scaffold Next.js 16 web app with Tailwind v4

Sets up apps/web with Next.js 16, React 19, Tailwind CSS v4 (postcss plugin
config, @import syntax), Jest + Testing Library, App Router layout and home page.
2/2 tests passing, build verified.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/app/page.tsx

@@ -0,0 +1,8 @@
+export default function Home() {
+  return (
+    <main className="flex min-h-screen flex-col items-center justify-center gap-4">
+      <h1 className="text-4xl font-bold tracking-tight">Insignia TOWER</h1>
+      <p className="text-lg text-gray-500">Community Knowledge Infrastructure Platform</p>
+    </main>
+  );
+}