Update environment configuration for PostgreSQL: Add new environment variables for NextAuth and PostgreSQL settings in .env file, update docker-compose.yml to utilize these variables, and enhance README documentation for environment setup. Ensure DATABASE_URL is constructed dynamically if not defined.

.gitignore

@@ -25,6 +25,7 @@ yarn-debug.log*
 yarn-error.log*
 
 # local env files
+.env
 .env*.local
 
 # vercel