Tighten Docker build and dependency audit

Dockerfile

@@ -3,8 +3,8 @@ FROM node:22-alpine AS builder
 
 WORKDIR /app
 
-COPY package.json ./
-RUN npm install
+COPY package.json package-lock.json ./
+RUN npm ci --no-audit
 
 COPY . .
 
@@ -21,7 +21,7 @@ ENV NODE_ENV=production
 COPY backend/package.json backend/package-lock.json ./
 
 # Install dependencies
-RUN npm ci --omit=dev
+RUN npm ci --omit=dev --no-audit
 
 # Copy backend source directly into root
 COPY backend/index.js ./index.js