fix(auth): update backend URL and API endpoint for authentication

frontend/auth.ts

@@ -1,7 +1,7 @@
 import NextAuth from 'next-auth';
 import Credentials from 'next-auth/providers/credentials';
 
-const BACKEND_URL = process.env.NEXT_PUBLIC_API_URL ?? 'http://recipe-api:3000/api';
+const BACKEND_URL = process.env.NEXT_PUBLIC_API_URL_INTERNAL ?? 'http://recipe-api:8080';
 
 export const { handlers, auth, signIn, signOut } = NextAuth({
   providers: [
@@ -13,7 +13,7 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
       async authorize(credentials) {
         if (!credentials?.username || !credentials?.password) return null;
         try {
-          const res = await fetch(`${BACKEND_URL}/auth/login`, {
+          const res = await fetch(`${BACKEND_URL}/api/auth/login`, {
             method: 'POST',
             headers: { 'Content-Type': 'application/json' },
             body: JSON.stringify({