fix: update CORS to use site's origin on production

backend/.env.example

@@ -1,3 +1,4 @@
+NODE_ENV=development
 MONGO_DB=mongodb://localhost:27017/urlMinify
 SECRET=secret
 AUTH_SECRET=secret

backend/index.js

@@ -10,9 +10,14 @@ require('dotenv').config()
 const app = express()
 
 app.use(express.json())
-app.use(cors({
-   origin: 'http://localhost:3000'
-}));
+app.use(
+   cors({
+      origin:
+         process.env.NODE_ENV?.trim() === 'development'
+            ? 'http://localhost:3000'
+            : 'https://minfy.xyz',
+   })
+)
 
 app.use(json())
 app.use(