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/types/next-auth.d.ts

@@ -0,0 +1,39 @@
+import { Role } from "@prisma/client";
+import "next-auth";
+import "next-auth/jwt";
+
+declare module "next-auth" {
+  interface Session {
+    user: {
+      id: string;
+      email: string;
+      tenantId: string | null;
+      roles: Role[];
+      isSuperAdmin: boolean;
+      firstName: string;
+      lastName: string;
+    };
+  }
+
+  interface User {
+    id: string;
+    email: string;
+    tenantId: string | null;
+    roles: Role[];
+    isSuperAdmin: boolean;
+    firstName: string;
+    lastName: string;
+  }
+}
+
+declare module "next-auth/jwt" {
+  interface JWT {
+    id: string;
+    email: string;
+    tenantId: string | null;
+    roles: Role[];
+    isSuperAdmin: boolean;
+    firstName: string;
+    lastName: string;
+  }
+}