Add Docker Compose deployment

- Dockerfile: Node.js 20 Alpine, single-stage build
- docker-compose.yml: backend + nginx, named volume for SQLite
- server.js: updated for Docker (env vars for PORT/DATA_DIR)
- nginx.conf: updated for Docker networking (backend hostname)
- README.md: full deployment instructions

deploy/nginx.conf

@@ -0,0 +1,22 @@
+server {
+    listen 80;
+    server_name _;
+
+    # Serve frontend static files
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # API proxy to Node backend
+    location /api/ {
+        proxy_pass http://backend:3000/api/;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+    }
+
+    # Static files - SPA fallback
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+}