feat: add Docker configuration for deployment

docker-compose.yml

@@ -0,0 +1,23 @@
+services:
+  web:
+    build: .
+    container_name: simplenote-web
+    restart: unless-stopped
+    ports:
+      - "${SIMPLENOTE_PORT:-3000}:3000"
+    environment:
+      - NODE_ENV=production
+      - PORT=3000
+      - ADMIN_TOKEN=${SIMPLENOTE_ADMIN_TOKEN}
+      - DATA_ROOT=/app/data
+      - CORS_ORIGIN=${SIMPLENOTE_CORS_ORIGIN:-*}
+    volumes:
+      - simplenote-data:/app/data
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://localhost:3000/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+
+volumes:
+  simplenote-data: