Update Dockerfiles to Node 20 for Next.js compatibility

api/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:18-alpine
+FROM node:20-alpine
 
 WORKDIR /app
 

client/Dockerfile

@@ -1,11 +1,11 @@
-FROM node:18-alpine AS builder
+FROM node:20-alpine AS builder
 WORKDIR /app
 COPY package*.json ./
 RUN npm ci
 COPY . .
 RUN npm run build
 
-FROM node:18-alpine AS runner
+FROM node:20-alpine AS runner
 WORKDIR /app
 
 ENV NODE_ENV production