deploy: split into dev/prod with separate Shopify configs and containers

- shopify.app.toml -> shopify.app.dev.toml (domain: invoice-app-dev.linumiq.com)
- New shopify.app.prod.toml will be created via shopify app config link --config prod
- docker-compose split into deploy/docker-compose.{dev,prod}.yml with distinct
  container names (linumiq-invoice-{dev,prod}), images, env files and bind mounts
- Caddyfile snippet maps both subdomains to their respective containers
- .env.{dev,prod}.example templates committed in deploy/
- deploy/README.md documents the layout and day-to-day workflow

deploy/docker-compose.prod.yml

@@ -0,0 +1,29 @@
+services:
+  app:
+    build:
+      context: ..
+      dockerfile: Dockerfile
+    image: linumiq-invoice:prod
+    container_name: linumiq-invoice-prod
+    restart: unless-stopped
+    env_file:
+      - .env.prod
+    environment:
+      # SQLite file lives on a bind mount so it survives image rebuilds.
+      DATABASE_URL: "file:/data/prod.sqlite"
+      NODE_ENV: production
+      PORT: "3000"
+    volumes:
+      - /docker/linumiq-invoice/prod/data:/data
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://127.0.0.1:3000/healthz", "||", "exit", "0"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+    networks:
+      - caddy_net
+
+networks:
+  caddy_net:
+    name: caddy_net
+    external: true