build(docker): add multi-stage Dockerfile with nginx and docker-compose

Add containerization support for production deployment:
- Multi-stage Dockerfile using Bun for build and nginx for serving
- docker-compose.yml for container orchestration
- nginx.conf with gzip compression, caching headers, and security headers

docker-compose.yml

@@ -0,0 +1,15 @@
+services:
+  ui:
+    build: .
+    container_name: gatehouse-ui
+    ports:
+      - "8080:8080"
+    environment:
+      - VITE_API_BASE_URL=${VITE_API_BASE_URL:-http://localhost:5000/api/v1}
+    restart: unless-stopped
+    stop_grace_period: 10s
+    logging:
+      driver: "json-file"
+      options:
+        max-size: "10m"
+        max-file: "3"