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.

.env.example

@@ -0,0 +1,4 @@
+PORT=5001
+API_NINJAS_KEY=your_api_key_here
+SECRET_KEY=your_secret_key_here
+DATABASE_URL=sqlite://calorie_tracker.db

docker-compose.yml

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+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:

nixpacks.toml

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+[phases.setup]
+nixPkgs = ["nodejs", "python3", "gcc", "gnumake"]
+
+[phases.install]
+cmds = ["npm install"]
+
+[phases.build]
+cmds = ["mkdir -p data"]
+
+[start]
+cmd = "npm run seed && npm start"