update dockerfile for frontend

frontend/Dockerfile

@@ -1,16 +1,19 @@
-FROM node:18
+FROM node:18-alpine
 
 WORKDIR /app
 
+# Copy package files & install deps
 COPY package*.json ./
-RUN npm install
+RUN npm ci --only=production
 
+# Copy source code
 COPY . .
 
-# 🔒 Ubah kepemilikan dan pakai user non-root
+# 🔒 non-root user (aman di Kubernetes)
 RUN chown -R node:node /app
 USER node
 
 EXPOSE 3000
 
+# Jalankan React dev server / Express tergantung project kamu
 CMD ["npm", "start"]