chore: add deployment and environment configuration files

Add .env.example for environment variable reference, nixpacks.toml for Nixpacks deployment, and docker-compose.yml for containerized deployment. These files provide necessary configuration for running the application in different environments.

docker-compose.yml

@@ -0,0 +1,24 @@
+version: '3.8'
+
+services:
+  app:
+    build: .
+    ports:
+      - "5000:5000"
+    volumes:
+      - calorie_tracker_data:/app/data
+    environment:
+      - PORT=5000
+      - NODE_ENV=production
+      # Add other environment variables here or use an env_file
+      # - API_NINJAS_KEY=your_key_here
+      # - SECRET_KEY=your_secret_here
+    restart: always
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:5000/"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+
+volumes:
+  calorie_tracker_data: