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.

next.config.ts

@@ -0,0 +1,12 @@
+import type { NextConfig } from "next";
+
+const nextConfig: NextConfig = {
+  // This app lives inside the Laravel repo tree (which has its own lockfiles);
+  // pin the Turbopack root so Next doesn't infer a parent directory.
+  turbopack: { root: import.meta.dirname },
+  // Prisma + the MariaDB driver adapter are native/server-only — keep them out
+  // of the bundle (same approach as the habbo-next reference).
+  serverExternalPackages: ["@prisma/adapter-mariadb", "mariadb", "@prisma/client"],
+};
+
+export default nextConfig;