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/Dockerfile

@@ -0,0 +1,17 @@
+FROM node:20-alpine
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm install --omit=dev
+
+COPY server.js ./
+
+# Create data directory for SQLite
+RUN mkdir -p /app/data
+
+VOLUME ["/app/data"]
+
+EXPOSE 3000
+
+CMD ["node", "server.js"]