feat(sdk_signer): add multi-stage Dockerfile for containerized deployment

Dockerfile

@@ -1,3 +1,18 @@
+FROM node:18-slim AS builder
+WORKDIR /usr/src/app
+COPY package.json package-lock.json ./
+RUN npm ci
+COPY . .
+RUN npm run build
+
+FROM node:18-slim
+WORKDIR /usr/src/app
+COPY --from=builder /usr/src/app/dist ./dist
+COPY --from=builder /usr/src/app/package.json ./package.json
+COPY --from=builder /usr/src/app/node_modules ./node_modules
+EXPOSE 3000
+ENV PORT=3000
+CMD ["node","dist/index.js"]
 FROM node:20-alpine AS base
 
 # Install production dependencies only by default