feat(01-02): configure NextAuth.js v4 with credentials provider and JWT

- Install next-auth@4, bcryptjs, @types/bcryptjs, @types/jest
- src/types/next-auth.d.ts: extend Session/JWT with tenantId, roles, isSuperAdmin
- src/lib/auth-options.ts: CredentialsProvider + JWT/session callbacks, 24h maxAge
- src/lib/auth.ts: getServerSession() and getCurrentUser() server helpers
- src/app/api/auth/[...nextauth]/route.ts: NextAuth GET/POST handler
- src/middleware.ts: withAuth middleware protecting all routes except /login /signup /api/auth/*

src/app/api/auth/[...nextauth]/route.ts

@@ -0,0 +1,6 @@
+import NextAuth from "next-auth";
+import { authOptions } from "@/lib/auth-options";
+
+const handler = NextAuth(authOptions);
+
+export { handler as GET, handler as POST };