fix(security): complete security and delivery compliance remediation

frontend/Dockerfile

@@ -1,10 +1,14 @@
 # Stage 1: Build
-FROM node:18-alpine AS build
+ARG NODE_BASE_IMAGE=node:20-alpine
+ARG NGINX_BASE_IMAGE=nginx:alpine
+FROM ${NODE_BASE_IMAGE} AS build
 
 WORKDIR /app
 
 COPY package*.json ./
-RUN npm install
+ARG NPM_CONFIG_REGISTRY
+RUN if [ -n "$NPM_CONFIG_REGISTRY" ]; then npm config set registry "$NPM_CONFIG_REGISTRY"; fi \
+    && npm ci
 
 COPY . .
 
@@ -12,7 +16,7 @@ COPY . .
 RUN npm run build
 
 # Stage 2: Serve with nginx
-FROM nginx:alpine AS serve
+FROM ${NGINX_BASE_IMAGE} AS serve
 
 # Remove default nginx config
 RUN rm /etc/nginx/conf.d/default.conf