Scaffold Next.js 16 app + wire NextAuth Credentials to auth core

Minimal but real App Router app that builds (next build exit 0):
- src/lib/auth.ts: NextAuth v5 Credentials provider calling checkLogin()
  (argon2id/bcrypt + md5->argon2id upgrade gated by CONVERT_PASSWORDS), JWT
  session, /api/auth/[...nextauth] route handler.
- src/app: root layout, home (force-dynamic, reads hotel_name via siteSettings),
  /login client form (signIn).
- next.config.ts: pinned turbopack.root, serverExternalPackages for the Prisma
  MariaDB adapter; tsconfig set up for Next.

Routes: / (dynamic), /login, /api/auth. Verified: next build exit 0, 28 tests.
Still needs DB+APP_KEY to run auth end-to-end. i18n/middleware/pages to follow.

src/app/page.tsx

@@ -0,0 +1,17 @@
+import Link from "next/link";
+import { siteSettings } from "@/lib/services/site-settings";
+
+// Reads settings from the DB at request time — never at build.
+export const dynamic = "force-dynamic";
+
+export default async function HomePage() {
+  const hotelName = (await siteSettings.get("hotel_name", "Atom")) ?? "Atom";
+
+  return (
+    <main style={{ fontFamily: "system-ui", padding: "2rem", maxWidth: 640 }}>
+      <h1>Welcome to {hotelName}</h1>
+      <p>AtomCMS → Next.js conversion. Foundation, full Prisma schema and auth core are in place.</p>
+      <Link href="/login">Login →</Link>
+    </main>
+  );
+}