docs: update README for environment variable configuration and clarify usage in Next.js

docker: modify Dockerfile to set NODE_ENV from environment variable for flexibility

README.md

@@ -55,14 +55,17 @@ Checks the code for linting issues.
 
 ## ⚙️ Environment Variables
 
-Create a `.env` file in the root directory with the following variables:
+Create a `.env.local` file in the root directory with the following variables:
 
 ```
-REACT_APP_API_URL=https://back-dev.clinic-pro.ir
-REACT_APP_CLIENT_ID=NWuujdYHjtAtrhrk_zoWB3w0kyf56wRCOaY36MIqvbs
-REACT_APP_CLIENT_SECRET=trhrk_zoWB3w0kyf
+NEXT_PUBLIC_API_URL=https://back-dev.clinic-pro.ir
+NEXT_PUBLIC_CLIENT_ID=NWuujdYHjtAtrhrk_zoWB3w0kyf56wRCOaY36MIqvbs
+NEXT_PUBLIC_CLIENT_SECRET=trhrk_zoWB3w0kyf
+NODE_ENV=development # or production
 ```
 
+**Note:** In Next.js, environment variables that need to be accessible in the browser must be prefixed with `NEXT_PUBLIC_`. Variables without this prefix are only available on the server side.
+
 ## 🌐 Features
 
 - ✅ Responsive design using MUI and Tailwind
@@ -99,4 +102,3 @@ This project is private or under your preferred license.
 ---
 
 > Developed with ❤️ by the Nobat724 team.
-