Adding Environment Variable for User Settings

Add server-side environment variables to configure default values for user settings.

Priority: User Custom > Server Env Var > Hardcoded Default

Steps

1. Define Environment Variable

Create src/envs/<domain>.ts:

import { createEnv } from '@t3-oss/env-nextjs';
import { z } from 'zod';

export const get<Domain>Config = () => {
  return createEnv({
    server: {