feat: add Docker deployment support

- Multi-stage Dockerfile (Node build + Go build + Alpine runtime)
- docker-compose.yml with named volume for data persistence
- In-container Nginx reverse proxy (static files + API)
- Entrypoint script for graceful process management
- .dockerignore for optimized build context
- Updated README (zh/en) with Docker quick start and deployment docs

Closes #14

deploy/docker/entrypoint.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+set -e
+
+# Backend listens on internal port 8341, Nginx exposes 8340
+export BACKUPX_SERVER_PORT="${BACKUPX_SERVER_PORT_INTERNAL:-8341}"
+
+# Start Nginx in background
+nginx -g "daemon off;" &
+NGINX_PID=$!
+
+# Start BackupX backend
+/app/bin/backupx &
+APP_PID=$!
+
+# Trap signals for graceful shutdown
+trap 'kill $APP_PID $NGINX_PID 2>/dev/null; wait $APP_PID $NGINX_PID 2>/dev/null' SIGTERM SIGINT
+
+echo "BackupX started — Nginx :8340 -> Backend :8341"
+
+# Wait for either process to exit
+wait -n $APP_PID $NGINX_PID 2>/dev/null || true
+kill $APP_PID $NGINX_PID 2>/dev/null || true
+wait $APP_PID $NGINX_PID 2>/dev/null || true