Optimize frontend Dockerfile: npm cache mount, non-root nginx, healthcheck

frontend/Dockerfile

@@ -1,3 +1,5 @@
+# syntax=docker/dockerfile:1
+
 # Stage 1: Install dependencies (cached if package-lock.json unchanged)
 FROM node:24-alpine AS deps
 
@@ -9,7 +11,8 @@ ENV NODE_OPTIONS="--max-old-space-size=1024"
 # Copy package files first for better layer caching
 COPY package.json package-lock.json* ./
 
-RUN npm ci
+RUN --mount=type=cache,target=/root/.npm \
+    npm ci
 
 # Stage 2: Run tests (fails the build if tests fail)
 FROM deps AS test
@@ -37,5 +40,13 @@ WORKDIR /app
 COPY --from=builder /app/dist /usr/share/nginx/html
 COPY --from=builder /app/nginx.conf /etc/nginx/conf.d/default.conf
 
+RUN chown -R nginx:nginx /usr/share/nginx/html
+
+USER nginx
+
 EXPOSE 80
+
+HEALTHCHECK --interval=30s --timeout=3s --retries=3 \
+  CMD wget --no-verbose --tries=1 --spider http://localhost:80/ || exit 1
+
 CMD ["nginx", "-g", "daemon off;"]