fix: add FRONTEND_URL to environment variables and create .env.example file

.env.example

@@ -0,0 +1 @@
+FRONTEND_URL=https://yourdomain.com

.gitignore

@@ -1,3 +1,4 @@
+.env
 backend/test_data/db/children.json
 backend/test_data/db/images.json
 backend/test_data/db/pending_rewards.json

docker-compose.yml

@@ -9,6 +9,7 @@ services:
       - "5001:5000" # Host 5001 -> Container 5000
     environment:
       - FLASK_ENV=production
+      - FRONTEND_URL=${FRONTEND_URL}
     volumes:
       - chores-app-backend-data:/app/data # Assuming backend data storage; adjust path as needed
     networks: