Add .env.example file and update docker-compose configurations for environment variables

.env.server.example

@@ -0,0 +1,23 @@
+# Server .env file for Development Environment
+# 
+# Instructions:
+# 1. SSH to your server: ssh webmaster@YOUR_SERVER_IP
+# 2. Create directory: mkdir -p /var/www/merchbay_admin_dev
+# 3. Create this file: nano /var/www/merchbay_admin_dev/.env
+# 4. Copy the content below (fill in YOUR_DB_PASSWORD)
+# 5. Save and secure: chmod 600 /var/www/merchbay_admin_dev/.env
+
+APP_ENV=development
+APP_DEBUG=true
+APP_URL=https://dev-admin.merchbay.app
+DB_HOST=mysql
+DB_PORT=3306
+DB_DATABASE=merchcbay_db
+DB_USERNAME=crewapp
+DB_PASSWORD=YOUR_DB_PASSWORD_HERE
+DOMAIN=dev-admin.merchbay.app
+
+# Notes:
+# - DB_HOST=mysql (your MySQL container name on crew-app-net network)
+# - Replace YOUR_DB_PASSWORD_HERE with your actual MySQL password
+# - This file should NEVER be committed to git